Introduction to Butterflies
Butterflies are extremely important members of the natural world. The irreplaceable position comes from their role as pollinators, without which the ecosystem cannot function. They drink nectar and other fluids, basically any liquid that can be dissolved in water. Biologically, butterflies are insects that belong to the large animal phylum Arthropoda. An adult butterfly has six joined legs, three main body segments- the head, thorax and adbomen-as well as four wings.
Along with the more numerous moths and skippers, true butterflies make up the order Lepidoptera. Within the order, true butterflies and skippers, which can be called by a jointed name “butterfly”, are seperated from moths. And true butterflies and skippers are further divided into two superfamiles, which we will go into details in later chapter.
A lepidoptera has a …long…life….cycle… It has a complete metamorphosis which includes four distinctive stages: the ovum, larva, pupa, and imago. The larva is the only stage in which growth occurs. Ova, pupae and adults do not grow.
What is it?- True Butterfly, Skipper & Moth
First there is an important question: why do we need to tell true butterflies, skippers and moths apart? With a pair of beautiful wings and curly antennae, hovering over flowers, don’t they all look alike? If most people just cannot tell the difference between them because those differences are not obvious enough, then why don’t we categorize them into the same kind? To answer this question let’s look up what exactly they do belong to. Biologically speaking, true butterflies, skippers and moths are all under the order of Lepidoptera, but if we further divide them into superfamilies, they go to different branches. While true butterflies belong to the superfamily of Papilionoidea, skippers belong to the superfamily of Hesperioidea and the moths belong to the superfamily of Sphingoidea. So as much alike as they are from general appearances, their genes are fundamentally different and if we make a comparison, they are different in many ways even in terms of appearances.
Perhaps it is a little bit easier for the general public to tell true butterflies from the other two, because common species of true butterflies tend to be larger in size and pretties in color. Such method can be true sometimes but technically not valid.
Below are some examples of how to differentiate
Moths can be much larger than some species of butterflies.
MOTH: Five-spotted hawk moth or tomato hornworm
TRUE BUTTERFLY: Gulf fritillary
And even some skippers can be larger than some true butterflies.
SKIPPER: Dion skipper
BUTTERFLY: Striped hairstreak
But there is one thing correct about the common size theory:
True butterflies tend to have long antennae and full wings. But more importantly, their bodies tend to be narrow and slender, while skippers and moths have stout bodies.
TRUE BUTTERFLY: European cabbage butterfly or imported cabbage worm
MOTH: Forage looper or clover looper moth
Besides size, another distinctive characteristic is their wings.
True butterflies tend to have brightly colored full wings while skippers have short triangular wings and are most often a shade of tawny-orange, brown, black, or gray. And moths tend to have a mixed feature of those two.
BUTTERFLY: Palamedes swallowtail
SKIPPER: Mottled dusky wing
MOTH: Oldwife Underwing
Besides their apearances, of course there are also other ways to distinguish members of the three superfamilies. They have different daily routine and sleep schedules.
True butterflies and skippers tend to fly during the day while moths are mostly nocturnal.
TRUE BUTTERFLY: Great spangled fritillary
MOTH: luna moth
Resting postures are also another useful method.
Butterflies tend to hold the wings vertically over the back while moths may either fold the wings tentlike over the back, or wrap them around the body, or extend them to the sides. Skippers hold their wings at different angles.
BUTTERFLY: viceroy butterfly
Some true butterflies, skippers, and moths have preferences for certain plants during a certain time of the year, which can help to identify them. Here is a list of such plants and their pollinators:
Wild Plum: Brown Elfin, Spring Azure, Grape-vine Epimenis
Pussy’s Toes: Pine Elfin
Wild Gooseberry: Brown Elfin, Hummingbird Moth, Bumblebee Moth
Bird’s foot Violet: Cobweb Skipper
White Sweet Clover: Banded Hairstreak, Hickory Hairstreak, Striped Hairstreak
Indian Hemp: Northern Hairstreak
Butterfly Weed: Coral Hairstreak
Pale-purple Coneflower: Regal Fritllary, Arogos Skipper, Ottoe Skipper
Plumbago or Leadwort: Cloudless Sulphur
Heath Aster: Dog Face, Leonardus Skipper
Common Species of Skippers in Missouri
The skippers are a large worldwide group containing several thousand species. The common name refers to the fast darting flight of the adults. Skippers have stout bodies and relatively small wings. The club of the antenna has a slender, recurved tip-the apiculus. The larvae have rather plain, dull colored bodies with large, distinctively patterned heads. The prothorax is very slender, which makes the head appear even larger.
- Status: Breeding resident found in all regions of the state
- Larva: Bright yellowish green, head reddish brown with two orange eyespots
- This is the largest skipper in Missouri. (As described before, skippers can be larger than butterflies!) The silver-spotted skipper is a common species of brushy fields, roadsides and city yards where it is easily recognized by the distinctive white patch on the hind wing beneath. There are three generations a year, with adults flying from early April to mid-October. Adults visit shrubs, darting out at any passing butterfly.
Hoary Edge—HIGHLIGHT: we may see their larva during spring semester
- Status: Breeding resident found mostly in the Ozarks and Ozark Border counties
- Larva: Pinkish buff with gray blotches, a gray mid-dorsal line and two pale subdorsal lines; head deep reddish purple with stiff white hairs.
- The hoary edge is common in open woods and along roadsides throughout the Ozarks. There are several broods, with the flight period beginning in early May and ending in October(so we may not see their adults) Adults visit flowers, especially bergamot. The underside pattern of the hind wing distinguishes this species from the silver-spotted skipper, which it resembles on the upper surface of the wing.
Southern Cloudy Wing
- Status: Breeding resident found throughout Missouri from mid-April to mid-October
- Larva: Brown, tinged with olive green; head black
- The southern cloudy wing is common and widespread in open woodlands, old fields and along roadsides. Males are found perching in open areas, while both sexes frequent a wide variety of flowers. Southern cloudy wing, northern cloudy wing and confuse cloudy wing are very close in size and pattern. Northern cloudy wing has a costal fold on the forewing, which is lacking on the other two. The color and pattern on the hind wing beneath is fairly distinctive in fresh specimens. Southern cloudy wing and Northern cloudy wing are widespread and common, while Confused cloudy wing is uncommon and found mostly in the southern Ozarks.
Northern Cloudy Wing
- Status: Breeding resident found in all regions of Missouri from April to September
- Larva: Green with a darker mid-dorsal line and two pinkish lines along the sides; head black
- This skipper is especially common in and near woodlands. Males perch on trees and shrubs, darting out at anything by that remotely resembles a female of the species. Northern cloudy wing sometimes gathers in numbers at muddy places along roads adn in creek beds. The adults are attracted to flowers, especially red clover, wood betony and wild bergamont.
Cobweb Skipper—HIGHLIGHT: we may see their larva during spring semester!
- Status: Single-brooded species native to the Ozark region in Missouri
- Larva: Grayish brown with lavender overcast; head dark purple with pale orange lines
- The cobweb skipper is found in Ozark glades and old fields with an abundant growth of the larval food plant. Adult fly from mid-April into May and can be found on early wildflowers such as the wild hyacinthm wild strawberry, rose verbena and dwarf larkspur. The larvae develop slowly during the summer, aestivating deep within the base of the plants during hot, dry spells and eventually hibernating through the winter with pupation occurring the following spring.
Dusted Skipper—HIGHLIGHT: we may see their larva during spring semester!
- Status: Breeding resident found in local colonies in the Ozarks.
- Larva: Pale pinkish lavender; head reddish purple with white hairs
- Dusted Skipper is a very local species found only in woodland clearings and cedar glades in the Ozarks. Males spend much of their time perching on plants, watching for females. Both sexes visit mant species of spring wildflowers. The larvae aestivate during the hot summer months and hibernate over winter, spending about ten months in the larval stage. The adults fly for only a few weeks in late April and May.
Common Species of True Butterflies in Missouri
(Since there are so many families under the superfamily of Papilionidae, I will only introduce one representative of each family.)
*family papilionidae–The Swallowtails
The swallowtails are a worldwide family of medium-to large-sized butterflies. The family contains about 700 species, with the greatest number found in the tropics, Most North American species have tail-like projections on teh hind wings-hence the common name. The larvae differ greatly from species to species. Some have a pattern of realistic eyespots on the throax; one in our area has a long, fleshy protuberances extending from the body. One feature all swallowtail larvae have in common is a Y-shaped organ that protrudes from the throax behind the head whenever the larva is disturbed. It emits a strong, rather repulsive odor which acts as a defense mechanism against enemies. Our species pupate suspended by a silken girdle around the throax and a pot of silk at the tip of the abdomen. All of the species found in Missouri hibernate as pupae.
- Status: Breeding resident in all areas of the state.
- Larva: Bluish green, body crossed with yellow and white bands, a wider black band across the humped third segment of the throax.
- With its long tails and distinctive pattern, the zebra swallowtail can be confused with no other North American butterfly. Zebra Swallowtail is a forest species and seldom wanders very far from its woodland haunts. It is attracted to many flowers and sometimes gathers in groups at mud puddles and in creek beds. There are several broods; spring specimens are smaller, with shorter tails, than those emerging later. The flight period extends from late March to October.
The pieridae are worldwide in occurance, with nearly 2,000 known species. Most are yellow, white or orange with black markings. Some species gather in great numbers at moist places, while others are known to migrate vast distances. The word “Butterfly” probably owes its origin to the yellow color of European sulphurs. Larvae are normally green, rather slender and without projections, but are often covered with fine down. Pupae are suspended by a silken girdle and cremaster, like the swallowtails.
- Status: a summer resident producing two or more generations in Missouri.
- Larva: Yellowish green with black dots and a yellow line along each side.
- This is a large yellow butterfly seen flying rapidly in a southeastern direction in late summer and fall. Unable to survive northern winters. This southern species migrates north each year to breed wherever females find suitable food plants, returning south each fall. Numbers vary greatly from year to year. The cloudless sulphur is often seen at moist places and visits a great variety of flowers. Leadwort and perennial Phlox are highly attractive to this species. This is one of the few butterflies that visits tube flowers such as four-o’clocks, petunias and trumpet vine.
Several thousand members of this family are found throught the world. Most are small-in fact, the smallest butterfly in North America belongs to this family. Many have iridescent copper or blue coloring. The hairstreaks have a fast, erratic flight and tiny tails on the hind wings. Lycaenidae larvae are usually short, flattened and covered with downy hair; sometimes they are likened to slugs or sowbugs. In the larval stage many species are associated woth ants. The pupae are short and stout. They are attached by a silk girdle and the cremaster to a leaf of the food plant.
Red-banded hairstreak—HIGHLIGHT: we may see their larva during spring semester!
- Status: Multi-brooded resident species found mostly south of the Missouri River.
- Larva: Yellowish green with a bluish green dorsal line and a heavy covering of brownish hair.
- There are three broods of the red-banded hairstreak in Missouri; adults can be found from mid-April to October. It is locally common in open forests and brushy fields throughout the Ozarks but is rare and sporadic in other regions.Males perch on the leaves of trees and shrubs; both sexes visit flowers and moist places. The spring brood has more blue on the wings above than later generations.
This is the largest family of butterflies in the world, comprising several thousand species. Most are medium-to large-sized butterflies. The forelegs are greatly reduced and useless for walking. The larvae usually covered with spines and tubercles. The pupae hang from the cremaster only and frequently have metallic spots or tubecles.
Great Spangled Fritillary
- Status: Common breeding resident found in woodlands and wet meadows.
- Larva: Black with black spines, yellowish orange at the base; head nearly black with some orange across the top.
- This large, easily recognized species frequently strays to city yards and gardens in search of flowers. There is a single generation each year, with adults flying from mid-May to early October. The larvae feed at night on the leaves of violets, hiding during the day away from the plants; newly hatched larvae hibernate. Great spangled fritillary visits flowers, carrion, animal droppings and mud puddles.
A worldwide family comprising over 2,500 species. Most of the family members are shades of brown with numerous eyespots.The majority feed on grasses in teh larval stage. The adults seldom visit flowers but are attracted to tree sap, sugar bait, carrion and animal droppings. Larvae are usually dull colored, in shades of green and brown, and have the last abdominal segment forked.
Southern Pearly Eye
- Status: Resident in southern Missouri where a few isolated colonies are known.
- Larva: Thicker in the middle, tapering to the ends, anal segment forked, body color yellowish green, one pair of red-tipped horns on last segment; head with shorter pair of red-tipped horns.
- This butterfly is very local in southern Missouri, where it is found in close association with cane beds. Typical southern pearly eye habitats are shady areas along and near streams where thick stands and tree trunks, frequently walking and turning in different decaying fruit, carrion adn animal droppings and often gather at moist spots. Females are frequently found resting on the food plant. Pearly eyes fly later in the day than most butterflies and are active until dusk.
Chiefly a tropical and subtropical family of about 300 species. The Danaids are protected species containing toxic, distasteful fluids. The butterflies are large, rather slow-flying and disctinctly colored. They feed solely on milkweeds in the larval stage, but they pollinate many different flowers when adults . The larvae are striped with yellow, black, and white and have a pair of fleshy tentacles at the front and back. The green pupae hang from the cremaster along and are usually decorated with gold or silver dots.
Milkweed Butterfly or Monarch
- Status: Summer resident only
- Larva: White with black and yellow transverse bands; head white with yellow and black markings; a pair of long, black, fleshy filaments on the thorax and a shorter pair near the end of the abdomen.
- The monarch is probably the best-known butterfly in North America. In the fall it migrates southward in huge flocks of hundreds, thousandsm or millions of specimens, which are often publicized in the news media. The northward migration in teh spring is a more gradual, individual event that usually goes unnoticed. The monarch is a protected species mimicked by the viceroy. Several broods are produced in Missouri during the summer and fall months. The adults visit a wide variety of flowers; New England aster is especially attractive to this species. The flight is rather slow and gliding, belying its ability to travel thousands of miles. The monarch’ body is very tough and rubbery. A predator can pinch the monarch hard enough to find out it is disatsteful; after being discarded the monarch can still fly away unhurt.
Common Species of Moth in Missouri
This is a cosmopolitan family of about 800 species, most of which are large moths. Their large bodies have powerful muscles. The forewings are long and narrow, while the hind wings are very small. The moths have a strong, rapid flight, clocked at speeds as high as 30 mph. Some species are day-flying, and becaese of their habit of hovering in front of flowers while feeding, are sometimes mistaken for hummingbirds. The tongue is strong, and long enough to reach the nectaries of deep-throated flowers. The larvae often rest with the head and throax reared up in a sphinixlike position. Fifty-six species of sphinx moths have been recorded from Missouri.
Pink-spotted Hawk Moth
- Status: A regular visitor to Missouri each fall, occasionally breeding in the southern countries.
- Larva: Color variable, seven pale, oblique stripes on the sides, black dorsal spots on the thorax; head with four vertical stripes.
- This attractive hawk-moth is sometimes a pest on sweet potatoes in the southern states. The adults visit flowers, especially the deep-throated species. In Missouri there are records from June to mid-November.
Approximately 1,100 species of Saturniidae have been described, mostly from tropical and subtropical regions of the world. These moths are medium-to large-sized. Many have patterns of eyespots on the wings, and some have long tails on the hins wings. The females attract males by releasing pheromones. Males are highly sensive to pheromones, and in field experiments have located females from several miles away. The mouth parts of adults are greatly reduced and most species do not feed in this stage. The adult span is short: two weeks or less on the average. All of our species overwinter in the pupal stage.
Luna or Moon Moth
- Status: Common, sometimes abundant species found throughout the state; especially in decideous forests.
- Larva: Bright green, segments sometimes convex with narrow yellow lines between, a yellowish lateral band below spiracles, three lateral rows of reddish tubercles on each side; head brownish; a thin, silken cocoon is spun among leaf litter on the ground.
- The beautiful luna’s disctinctive green color and long tails distinguish it from all other Northe American moths. There are three broods in Missouri, with adults flying from early April to August. The calling time occurs around midnight.
The Noctuidae is a huge, worldwide family of moths numbering as many as 24,000 species. There are more than 700 members in Missouri; it is by far the largest family in the state. Naturally there is great variation in the color, pattern, size and habits of the species occurring in Missouri. Most noctuids are medium-sized; a few are very small, and one species of the New World tropics has a wingspan of up to 12 inches. The adults have well-developed tongues and feed on flower nectar, tree sap, ripe fruit and sometimes on carrion and animal droppings. Species may resemble green or dried leaves, the dark trees, lichens and mosses.
- Status: Abundant resident species found in all areas in Missouri.
- Larva: Resembles Catocala; finely striped in shades of brown with black tubercles, ventral area paler with some reddish-brown to black dots.
- This very common moth will be found in both woodlands and in city yards. The adults are frequently found on flowers and fairly swarm to sugar bait. The pupae, and apparently some adults, hibernate. There are Missouri records for every month of the year but January.
There are over 600 species of plume moths around the world, although the number of species for Missouri is not known. This family is very distinctive due to its posture, holding their wings out at right angles to their bodies. All of the species in this family are small and are often found on plants during the day, but they also come out to lights at night. On many of the species, the legs have long spines.
- Status: Common resident specious found throughout the state
- Larva: Yellow-green with broad yellow-white stripes along their sides
- This moth can be found in many habitats, but it is most commonly encountered at lights in suburbs. They are very small. They have been found in the state in every month other than January. The larva eat leaves of plants, including morning glory.
Conservation and Collecting Methods
Butterflies, with their sparkling color patterns and elegant gestures, are beloved by scientists as well as the general public. From a reservation ecology point of view, they are also valuable as pollinators that can help with local plant reservation. But researchers have observed decline of the diversity and population of butterflies, which may be caused by damage to their natural habitat and pollution from insecticide and herbicide. It is necessary to encourage more people to pay more attention to butterflies’ living condition. Collecting butterflies is one of the most effective and eco-friendly ways to bring them to the view of the public. The reason why it’s eco-friendly is that “generally speaking collecting has no appreciable effect on the stability of Lepidoptera population”. Then what is the correct way to collect butterflies?
One of the most useful ways to attract Lepidoptera is by making a mixture called “sugar bait” and dabbing it every few days on post, rocks or tree trunks. You can make a “sugar bait” with a can of beer, two pounds of sugar, two cups of molasses or syrup and two pounds of well-ripened fruit. Stir well and let them ferment in the sun for a day. It will attract butterflies at day and moths at night. Some people also choose to catch butterlies by nets and it is surely a good method as long as you pay attention to safety. After you catch them, the safest way to kill your specimen in the field is to carry a can of lighter fluid and put a drop on the head of each specimen as it is caught. Store the specimen you killed with envelops and be sure to use forceps to handle your specimens. When you go back home, put your insects on a spreading board. Insert the insect pin into the center of the thorax and push it straight through to within about three-eighths of an inch of the pin head. Normally you can use size 3 pins for most moths and butterflies. For particularly small ones you can use size 1 or 0 instead. After the insect is fully dried, measure their lengths, weight, etc. Put a data lable on each specimen and preserve them in a storage box.
As one of the most well-known Northern American butterfly species, the monarch has been much observed and researched on. It’s a member of the Danaidae family, the monarch tends to be large and slow-flying, a characteristic that has been developed to adapt to long-distance migration. Yes, butterflies can migrate, just like the birds and whales. Some individual butterflies travel upwards of 3,000 miles and can fly at altitude as high as 10,000 feet. They are the only butterfly species to make such a long, two-way migration every year. Their offspring return each winter to the same winter roots and even to the same trees used by previous monarch generations– even though the migrating monarchs die before returning. (Credit: NPS)
Surely it is one of the most unique and amazing migration events that occurs each autumn when thousands of the monarch butterflies migrate to the warm mountains of central Mexico and the coastal regions of southern Carolina. (Credit: NPS) If the monarch has spent the summer easts of the Rocky Mountains, it will travel to the Sierra Madre Mountains of Mexico. Here, they are known as Mariposa monarca and will spend the winter days from October to the late March in the warm, unique habitat of oyamel fir trees. If the monarch has spent the summer west of the Rocky Mountains, it will travel a shorter distance, to the many groves of Monterey pine, Tasmanian bluegum eucalyptus and Monterey cypress found along the coasts from northern to southern Califonia. (Credit:USDA)
Once they reach the trees in which they will over-winter, the monarch butterflies will cluster together to stay warm. Tens of thousands of beautiful orange butterflies can cluster together in a single tree. Even though a single monarch weighs less than fractions of an ounce, the massive cluster of butterflies can exert a heavy weight on tree branches, which sometimes break from the combined weight of butterflies.(Credit: Linda&Dr. Dick Buscher)
Here are some links of research organizations that help with butterfly conservation.
Butterflies and Moths of North America
Missouri Botanical Garden-Our Butterfly Collection
Missouri Butterflies and Moths
Buscher, Dick and Linda. “In Photos: The Spectacular Migration of Monarch Butterflies.” Life Science, http://www.livescience.com/52513-monarch-butterflies-migration-photos.html.*
Caillin. “What’s the Difference Between Butterflies, Moths and Skippers?” Australian Butterfly Sanctuary, http://australianbutterflies.com/whats-difference-butterflies-skippers-moths/.*
Pyle, Robert Michael. “National Audubon Society Field Guide to North American Butterflies.” A Chanticleer Press Edition. Alfred A. Knopf, New York, September 1997.
Richard, J. and Heitzman, Joan E. “Butterflies and Moths of Missouri.” Edited by Kathy Love and LuAnne Larsen. Conservation Commision of the State of Missouri, 2006.
Butterfly body parts: http://kids.britannica.com/comptons/art-53025/Like-other-insects-moths-and-butterflies-have-four-wings-six
Butterfly life cycle: http://www.zoomschool.com/subjects/butterfly/activities/printouts/lifecycle.shtml
Oldwife Underwing: http://bugguide.net/node/view/1108266/bgpage
Day butterfly: http://bugguide.net/node/view/819100/bgimage
Night moth: https://weaverinthewoods.wordpress.com/2014/06/17/luna-moth-diaries/
Pink-spotted hawk moth: http://www.silkmoths.bizland.com/Sphinx/acingula.htm
Five-spotted hawk moth: http://davesgarden.com/community/forums/fp.php?pid=3833700#b
Gulf fritillary: http://7-themes.com/6954794-gulf-fritillary-butterfly.html
Dion skipper: http://www.butterfliesandmoths.org/species/Euphyes-dion
Striped hairstreak: https://wisconsinbutterflies.org/butterfly/species/38-striped-hairstreak
European cabbage butterfly or imported cabbage worm: http://www.glovernursery.com/butterflies-around-the-wasatch-front/
Forage looper or clover looper moth: http://somethingscrawlinginmyhair.com/2015/05/16/cloverforage-looper/
Palamedes swallowtail: http://butterfliesathome.com/palamedes-swallowtail-butterfly.htm
Mottled dusky wing: https://www.ontario.ca/page/mottled-duskywing-government-response-statement
Tawny Emperor: http://www.botwf.org/page112.html
Sliver-Spotted Skipper: https://wisconsinbutterflies.org/butterfly/species/112-silver-spotted-skipper
Hoary Edge: http://www.marylandbutterflies.com/pages/Spreadwingedskippers_HoaryEdgeSkipper.html
Southern Cloudy Wing: http://www.pwconserve.org/wildlife/butterflies/southerncloudywing.html
Northern Cloudy Wing: http://novascotiabutterflies.ca/ss.cgi?s=nocl
Dusted Skipper: http://www.naba.org/sightings/archives/oct2006/dusted.htm
Zebra Swallowtail: http://www.animalspot.net/zebra-swallowtail-butterfly.html
Cloudless Sulphur: http://lemonbayconservancy.org/summer-butterfly-delights-purple-cone-flowers/
Red-banded hairstreak: https://www.flickr.com/photos/44947946@N06/5944325256
Great Spangled Fritillary: https://www.wunderground.com/wximage/basicbill/170
Southern Pearly Eye:http://michaelbeohm.tripod.com/id14.html
Milkweed Butterfly or Monarch: http://www.techtimes.com/articles/50518/20150505/researchers-to-attempt-demystifying-environmental-advantages-of-milkweed.htm
Luna or Moon Moth: http://www.biopix.com/indian-moon-moth-indian-luna-moth-actias-selene_photo-60854.aspx
Lunate Zale: http://picssr.com/tags/erebinae/page31
Emmelina monodactyla: http://bugguide.net/node/view/1166799/bgpage
Insect Case: https://manitobamuseum.ca/main/where-the-dead-things-are/
This page was written and created by Yilenda Dong
Lepidoptera: A large order of insects comprising the butterflies, moths, and skippers that as adults have four broad or lanceolate wings usually covered with overlapping and often brightly colored scales and that as larvae are caterpillars.
Larva: The immature, wingless, and often wormlike feeding form that hatches from the egg of many insects.
Pupa (Chrysalis): The dormant stage following the last larval moult.
Imago: Adult butterfly or moth.
Pheromones: Chemical substances highly attractive to males of certain species