Part 11

Isopoda Sowbugs, Pillbugs

Convex, many-legged animals having conspicuous antennae; several of the posterior segments short and joined rather closely to form an abdomen. Of the Illinois forms, about one-half are aquatic, living in streams and ponds. The others live in terrestrial situations that are humid and dark. They are frequently found under boards and in soil in greenhouses. One species of this group is Armadillidium vulgare (Latreille), fig. 68, which possesses the ability to curl up in a hard shell-like ball when disturbed. The isopods, relatives of crabs, shrimps, and crayfish, belong to the general group known as crustaceans. The crustacean groups are abundant in the ocean. In past geologic ages, the early ancestors of such predominantly terrestrial groups as insects and spiders resembled ancestors of the present crustacean marine forms.

Amphipoda Small Water Shrimps

Humpbacked, many-legged crustaceans, fig. 69, that are, unlike the isopods, flattened from side to side like the fleas. They are all aquatic but are seldom found swimming in open water; they prefer to live in tangled masses of vegetation, under stones or logs, and among debris in the very shallow water where it touches the bank. These little shrimps are never more than about one-half inch long and are frequently collected in large numbers along with aquatic beetles. As is the case with the aquatic sowbugs, certain species of amphipod shrimps occur in subterranean water sources and frequently are found in wells. Most of these species are blind.

Scorpionida Scorpions

Animals belonging to the spider group; characterized by a pair of stout pincers at the end of each front leg and a long tail-like extension of the abdomen ending in a sharp sting, as in Centruroides vittatus (Say), fig. 70. They have fairly long bodies and five pairs of legs each, including the chelate pair. During the day they live under stones and bark, moving about at night in search of insects and other small organisms on which they prey. Many species occur in the Southwest; the range of one of these extends as far northeastward as southwestern Illinois.

Pseudoscorpionida Pseudoscorpions

Animals belonging to the spider group; characterized by a pair of stout pincers at the end of the front legs, as in Larca granulata (Banks), fig. 71. They have short, stout bodies, each with five pairs of legs including the chelate front pair, but unlike the true scorpions they have no tails or stings. The pseudoscorpions are sometimes found indoors in old books, looking for their prey of small insects. They occur in greater numbers in wooded areas.

Phalangida Daddy Longlegs, Harvestmen

Spider-like forms, each animal with a short, round body and four pairs of walking legs that in most species are very long, fig. 72. They occur chiefly in woods and may be found in numbers walking over foliage and logs; they are often found on bluffs and in shady places. They feed on decaying humus. A few Illinois forms that occur chiefly on bark have considerably shorter legs than the species that range more widely.

Araneida Spiders

Varied and well-known animals, each with four pairs of walking legs and a body divided into a cephalothorax (which combines the head and thorax) and abdomen. The spiders present a tremendous variety of shapes, some being round and fat, like the black widow, Latrodectus mactans (Fabricius), fig. 73, others being long and slender, mimicking ants. Others are crablike in shape; some that are long and slender are extremely rapid in their movements. Spiders appear practically everywhere. Certain species are domestic and are found only in houses. In Illinois the only poisonous species of any importance are the black widow spider, which is found in a variety of situations, and the recluse spider, Loxosceles reclusa Gertsch & Mulaik, which has been found in house basements in southern Illinois.

Acarina Ticks, Mites

Animals somewhat like the spiders but having no marked division between the cephalothorax and the abdomen. Each adult has four pairs of walking legs, although an individual of the very young stages has only three pairs. The mites are generally very minute and seldom are seen by the beginning collector. They vary greatly in general appearance. Many species are extremely destructive to stored produce, to live domestic animals, and to many groups of plants. Adults of the harvest mite and early stages of the chigger mite attack man persistently.

Ticks are larger than mites. All the species feed on warm-blooded animals, including birds and mammals. The commonest Illinois tick is Dermacentor variabilis (Say), fig. 74, which transmits the organism causing the often fatal disease called Rocky Mountain spotted fever. Although this disease occurs only infrequently in Illinois, hikers and others exposed to ticks on excursions into the out-of-doors should carefully examine their clothing and bodies and promptly remove any ticks they find.

Diplopoda Millipedes

Elongate animals each having a distinct head and a long, many-segmented body with two pairs of legs on every segment. The commonest Illinois representative is the large Parajulus impressus (Say), fig. 75, a robust, cylindrical, reddish species commonly found in rotten logs or moist leaf mold. Most species feed on decaying vegetable matter. A few occasionally do considerable damage in greenhouses.

Chilopoda Centipedes

Elongate animals, similar in general appearance to the millipedes but with only one pair of legs on each body segment. Many species are predacious, feeding on insects and other small animals in rotten logs and humus. Most familiar to the city dweller is the house centipede, Scutigera forceps Rafinesque, fig. 76; this is a common inhabitant of dark places in houses, where it runs about with incredible speed in search of the small insects upon which it feeds. Other species may be encountered under boards and stones in gardens, fig. 77. Some Illinois centipedes found in woody or rocky situations are 2 inches or more long. No chilopod group in this state is dangerous to human beings, but to the south occur centipedes nearly a foot long that may inflict serious bites.

THE STATE INSECT COLLECTION

Illinois is one of the very few states that maintain a large research insect collection. This collection is under the care and guidance of the Section of Faunistic Surveys and Insect Identification of the Illinois Natural History Survey. It is housed in the west part of the fireproof Natural Resources Building on the University of Illinois campus at Urbana, fig. 78. Begun about 1880, the collection has grown steadily until now it is the most extensive representative collection of the insect fauna of any state in the nation. The collection consists of over 5,500,000 specimens of insects housed in steel cabinets, fig. 79. The pinned collection includes about 750,000 specimens in trays. The collection preserved in alcohol contains over 3,500,000 insects including not only a great number of valuable adult insects but also a very useful collection of immature insects. The slide collection contains nearly 250,000 specimens mounted as permanent microscopic preparations. The papered and boxed material comprises more than 1,000,000 specimens of dried insects.

The most important use of the collection is for identification of insects known to damage crops, stored grains, and household articles, or to threaten human health. Important also is its use as a storehouse of information regarding the ecology, host relationships, and distribution of Illinois insects.

So large is the field of insect classification that many important gaps exist in our knowledge of the Illinois fauna. For maximum usefulness, the collection should contain a complete representation of the Illinois insect fauna, supplemented with as much additional North American material as can be obtained. This additional comparison material is frequently necessary to evaluate correctly the species occurring in the state. It is estimated that there are about 20,000 different species of insects in Illinois and 150,000 in North America. The collection contains representatives of over 15,000 Illinois species, and a great many other North American species useful as comparison material in the identification of Illinois forms.

Gifts to the collection of well-prepared material are greatly appreciated. Many of those already received have made vital contributions to the collection and added valuable records to the Natural History Survey files of insect distribution.

REPORTS ON ILLINOIS INSECTS

As a result of the accumulation of material and information in the faunistic collection, the Illinois Natural History Survey has published a number of reports dealing with various groups of insects and other animals in Illinois; other reports in this series are being prepared or planned. These reports are designed primarily for use of the advanced student in zoology and entomology. They contain information regarding the characteristics, habits, and distribution of the various species in the state, keys for their identification, and illustrations to assist in diagnosis of the structures used in identification. Because of their great abundance in both species and numbers, and their importance as pests, insects have been studied extensively and much has been written about them.

The following reports of Illinois insects and their relatives have been published by the Illinois Natural History Survey. Those marked "out of print" are unavailable at the Survey, but may be consulted at libraries or obtained from book dealers. Interested persons may obtain publications by writing to the Chief, Illinois Natural History Survey, Urbana, Illinois 61801.

The Oribatoidea of Illinois [Mites], by Henry E. Ewing. Out of print. The Chironomidae, or Midges, of Illinois, by J. R. Malloch. Out of print. A Preliminary Classification of Diptera, by J. R. Malloch. Out of print. The North American Species of the Genus Tiphia [Wasps], by J. R. Malloch. Out of print. The Pentatomoidea of Illinois [Stink Bugs], by Charles Arthur Hart. Out of print. Forest Insects in Illinois: I. The Subfamily Ochthiphilinae (Diptera, Family Agromyzidae), by J. R. Malloch. Out of print. Fall and Winter Stoneflies, or Plecoptera, of Illinois, by Theodore H. Frison. Out of print. The Plant Lice, or Aphiidae, of Illinois, by Frederick C. Hottes and Theodore H. Frison. Out of print. The Dermaptera and Orthoptera of Illinois, by Morgan Hebard. The Stoneflies, or Plecoptera, of Illinois, by T. H. Frison. Nearctic Alder Flies of the Genus Sialis (Megaloptera, Sialidae), by H. H. Ross. Out of print. The Plant Bugs, or Miridae, of Illinois, by Harry H. Knight. Studies of North American Plecoptera, With Special Reference to the Fauna of Illinois, by T. H. Frison. The Caddis Flies, or Trichoptera, of Illinois, by Herbert H. Ross. Out of print. The Leafhoppers, or Cicadellidae, of Illinois, by D. M. DeLong. The Pseudoscorpions of Illinois, by C. Clayton Hoff. The Mayflies, or Ephemeroptera, of Illinois, by B. D. Burks. A Synopsis of the Mosquitoes of Illinois (Diptera, Culicidae), by Herbert H. Ross and William R. Horsfall.