Top 20 Most Common Insects in Illinois

Celastrina argiolus ladon is a butterfly from the Lycaenidae family, the small pages, fire butterflies and blues. This subspecies used to be considered as a separate species, but in a revision it is classified as a subspecies of the blue tree. This revision is not accepted by all authors.

Red admiral (Vanessa atalanta) is a visually striking species of butterfly. Unusually territorial, males will compete for choice areas, and females will only mate with males that maintain their own territories. This butterfly is known for being particularly patient with human interactions, even to the point of perching on clothing or flesh.

Anopheles (/əˈnɒfɪliːz/) is a genus of mosquito first described and named by J. W. Meigen in 1818. About 460 species are recognised; while over 100 can transmit human malaria, only 30–40 commonly transmit parasites of the genus Plasmodium, which cause malaria in humans in endemic areas. Anopheles gambiae is one of the best known, because of its predominant role in the transmission of the most dangerous malaria parasite species (to humans) – Plasmodium falciparum. The name comes from the Ancient Greek word ἀνωφελής anōphelḗs 'useless', derived from ἀν- an-, 'not', 'un-' and ὄφελος óphelos 'profit'. Mosquitoes in other genera (Aedes, Culex, Culiseta, Haemagogus, and Ochlerotatus) can also serve as vectors of disease agents, but not human malaria.

Ochlerotatus triseriatus, also known by the synonym Aedes triseriatus, is a member of the true fly order (Diptera: Culicidae). It is called the eastern tree hole mosquito due to its predilection towards breeding in stagnant water that is found in natural holding containers such as tree holes. It is native to the eastern United States and southern Canada and favors hardwood habitats. It has been found as far south as the Florida Keys, as far west as Idaho and Utah, and as far north as Quebec and Ontario. This species has not yet been found in Europe, but it has the potential to spread through international trade. In 2004, it was found in a shipment of tires travelling from Louisiana to France, but it was identified and targeted with insecticides that truncated its spread. It is a known vector of La Crosse encephalitis and canine heartworm disease. In the laboratory, it has been found to vector several other viruses including yellow fever, eastern encephalitis, Venezuelan encephalitis, and western encephalitis. Because of its potential for international spread and its proclivity for transmitting disease, monitoring the distribution of this species is essential.

The great spangled fritillary (Speyeria cybele) is a beautiful butterfly that is orange in color and has a variety of spots on its body like a leopard. Females tend to be a bit darker than their male counterparts. Their caterpillars are black with orange spots and often caught feeding on violets. 

The silver-spotted skipper (Epargyreus clarus) constructs a series of nests throughout its development that depends on its growth stage. Its caterpillar form is considered a major homebody, as they rarely leave the spot they call home. When they are adults, males perch on high branches in order to claim and defend favorable territory. Unusually, silver-spotted skipper adults never visit yellow flowers.

The common Eastern Bumble Bee (Bombus impatiens) is one of the most important pollinator bees in North America. A decline in the bee population will lead to financial hardships for farmers and reduced food yield. Their efficiency in pollination and foraging comes from their ability to drop "traplines." These lines guide other bees to the correct path for food while informing them of depleted locations.

Adults have a distinctive bronze-colored, lyre-shaped pattern on the scutum, and larvae have a linear arrangement of branched frontal setae and a strongly spiculated anal saddle.

The viceroy (Limenitis archippus) is a butterfly that mimics the Monarch Butterfly. The viceroy is distinct because it is smaller than the Monarch. Still, it manages to use this to ward off most predators. There is also polymorphism, meaning that the colors of this butterfly can change depending on the territory.

The common wood nymph (Cercyonis pegala) is a brown butterfly that has eyespots located on it to assist in warding off predators, as they are pretty easily spooked by anything that looks like a giant face. Depending on the location, they may or may not come with the eyespots or additional yellow spots, giving them a good chunk of variance depending on growing environment.