University of Kentucky Entomology/Kentucky Critter Files/Identification Tips
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Kentucky's insects, spiders, and other arthropods


There are thousands of species of insects, spiders, and their relatives in Kentucky.  Identifying insects and spiders is a challenge even for experts, but on this page we will share some practical tips.

Important! The Kentucky Critter Files is designed to provide information for commonly encountered Kentucky arthropods, but it is not a complete scientific identification guide.  Even though we are always adding new pictures, there are thousands of insects and spiders that may never appear on this site.  In addition, the identifications on this site should be considered tentative: positive identifications require whole specimens and scientific identification keys.  Identifications based on pictures carry a HIGH chance for error.  Our pictures can help you with identification, but if you need positive identification of an insect or spider for medical, legal, or economic reasons, seek assistance from a professional pest control company or your local county extension office.

FIRST STEP: Is it an arthropod?
With the exception of Slugs, our special guest critters from the mollusk group (Phylum Mollusca), The Kentucky Critter Files is an on-line guide to common Kentucky arthropods.  Snails, worms, snakes, are not arthropods (although some people call them critters!).  So--the first thing that you want to do is make sure that your critter is an arthropod.  Arthropods include insects, spiders, millipedes, centipedes, daddy-long-legs, scorpions, crustaceans (crabs, lobsters, shrimp, roly-polies), and a few other animals.  All of these animals have 2 important things in common: they all have EXOSKELETONS and they all have JOINTED, SEGMENTED LEGS.  A snail, for instance, has an exoskeleton (a shell), but it has no legs, so it is not an arthropod.

SECOND STEP: Is it an insect?  A spider?  Something else?
If your animal has an exoskeleton and jointed legs, it must be an insect, a spider, or some other kind of arthropod.  The phylum Arthropoda is separated into a few different groups called "classes," and it is fairly easy to tell which class an arthropod belongs to.  In almost all cases , knowing the number of legs will tell you what kind of arthropod you have.  Listed below are the common arthropod classes that live in Kentucky, along with the characters that you need to know to identify them:

Insecta: Insects.  All insects have 6 legs, 3 on each side, plus 2 antennae and 3 main body parts (head, thorax, abdomen).  Insects are the only arthropods that ever have wings.

Arachnida: Spiders, scorpions, mites, ticks, daddy-long-legs.  All arachnids have 8 legs, 4 on each side, and 2 main body parts (cephalothorax and abdomen).  Arachnids never have antennae, but they do have 2 appendages near their mouths called "pedipalps" or "palps" that sometimes look like antennae.  A scorpions claws, for instance, are its pedipalps.  Arachnids also have fang-like mouthparts called "chelicerae."

Chilopoda: Centipedes.  Centipedes are multi-segmented arthropods with at least 10 body segments, most of which have 2 legs each (1 on each side).  Centipedes have 2 antennae and venomous fangs, which are actually the first pair of legs.  All centipedes are believed to be predators, and most are fast-moving.

Diplopoda: Millipedes.  Like centipedes, millipedes have multi-segmented bodies with at least 10 body segments, but most segments on a millipede have 4 legs each, 2 on each side.  Millipedes have 2 antennae, but no venomous fangs.  Most millipedes are slow-moving herbivores or scavengers.

Crustacea: Crayfish, shrimp, sowbugs, roly-polies.  Crustaceans have a variable number of legs, but most common species in Kentucky have either 10 legs (crayfish) or 14 legs (sowbugs and roly polies).  Most crustaceans have 4 antennae. Many crustaceans are aquatic, like the crabs and lobsters that live live in the oceans, but sowbugs and roly-polies are very common on land.

THIRD STEP: Okay, now what?
It is easy to determine what class of arthropod you have, but it gets tougher when you want to know what kind of spider, what kind of insect, or what kind of centipede, for instance.  On this site, the best way to find out what kind of insect or spider you have is by looking through the pictures and reading the descriptions.  We don't have pictures of every species, though, so you may want to check other resources.  Listed below are some books that can help:


Peterson Field Guide to Insects by Borror and White.  This guide contains technical identification information with detailed drawings. It is most useful for determining which scientific order or family an insect belongs to.  This book also contains a scientific picture key to insects.  Scientific keys are the definitive method to identify an organism, but they can be very hard to use with insects if you do not have a microscope.
National Wildlife Federation Field Guide to Insects and Spiders & Related Species of North America by Arthur V. Evans.  This is one of the newest guides to insects and their relatives, and one of the best.  It contains pictures and info for lots of insects and spiders, and it goes beyond to cover centipedes, millipedes, and other arthropods.
Simon & Schuster's Guide to Insects by Arnett & Jacques.  This guide contains pictures of many common insects.
National Audubon Society Field Guide to North American Insects & Spiders by Milne & Milne.  Like the Simon & Schuster guide, this guide has pictures of many common insects and spiders.
Peterson Field Guide to Beetles by White.  Like the Peterson Field Guide to Insects, the Guide to Beetles contains technical details for identifying beetles to the family level.

Peterson Field Guide to Eastern Butterflies by Opler.  This guide contains technical details for identifying most butterflies.  
Spiders and Their Kin by Levi & Levi.  This low-priced "Golden Guide" contains drawings of many common spiders, plus centipedes, millipedes, mites, ticks, and sowbugs.

Butterflies and Moths by Mitchell & Zim.  Like the Golden Guide to spiders, this guide is budget-priced and contains pictures of most common butterflies and moths.  


Also, visit our Links page for other websites that have pictures of insects and insect relatives.  Not all of the sites listed focus on Kentucky insects, but many of the insects that live in Kentucky occur in other parts of the United States as well.

FOURTH STEP: Practice and Repeat!
Sometimes, you will go through the steps listed above or you will use a scientific identification key, and you will not find the correct identity.  That's okay!  Just keep trying.  After you spend time observing insects outdoors and comparing those insects with pictures and by becoming familiar with scientific identification keys, you will find that you can identify most insects and spiders as soon as you see them.

IMMATURE ARTHROPODS: A word of warning
Like human youngsters, immature insects and spiders have trouble following the rules, even the rules of identification.  Many times on this website or in other guides you will find statements that say: "all insects in this family have 4 wings," or something similar.  These statements usually apply to ADULT arthropods only.  Immature arthropods often look completely different than the adults.  This makes insect identification very confusing, especially since most books and guides to identification don't include pictures or information about the immature stages.  One of the goals on the Kentucky Critter Files is to include pictures of insect larvae, nymphs, and even eggs and pupae whenever possible.  No guide can include pictures of every species and every life stage, however, so keep this in mind when identifying!  

Other Tips:  Don't try too hard to figure out what SPECIES an insect or insect relative is.  Identifying the species of an insect or insect relative is extremely difficult, even for experts.  Unless you need to know a species name for medical or scientific reasons, it is usually not necessary to know this information.  Instead, work on trying to determine what class, order, and family an arthropod belongs to.  If you can look at an insect or spider and determine what scientific family it belongs to, you are an accomplished entomologist! 


Original document: 25 May 2004
Last updated: 1 May 2008

All photos courtesy R. Bessin and B. Newton, University of Kentucky.

The Kentucky Critter Files are maintained by Blake Newton, Department of Entomology, University of Kentucky.

University of Kentucky Entomology/Kentucky Critter Files/Identification Tips