Insects are generally considered to be rare in the Upper Carboniferous Coal Measures. However, recent work in the Westphalian D of SW England suggests that many have been overlooked in the past. This is because wings, which are the most characteristic insect fossils, may be mistaken for detached ‘fern’ pinnules, which are much more common. The resemblance may be functional convergence rather than leaf-mimicry.
The earliest members of the class Insecta in the strict sense occur in the Upper Carboniferous. Eleven major divisions or orders are represented in the Coal Measures of which only four are still living. Primitively wingless insects (Archaeognatha) are present, relatives of familiar living insects such as the silverfish. There are numerous winged insects, some of which could fold their wings (Neoptera) and others which could not (Palaeoptera). Palaeopterous insects were more diverse than today. They include three extinct orders (Palaeodictyoptera, Megasecoptera, Diaphanopterodea) which were probably plant suckers like present clay bugs. Other extinct palaeopterous insects (order Protodonata) were probably aerial predators like modern dragonflies, and included some of the largest insects of all time (‘giant dragonflies’).
By far the most common neopterous insects were cockroaches (Blattodea) which outnumber all other insects in the Upper Carboniferous. This abundance is perhaps less surprising when one considers the general picture of the coal forests as warm, humid, and rich in organic matter. Another important neopterous group was the extinct order Protorthoptera, which is probably related only in part to extant Orthoptera (grasshoppers, crickets and locusts). There is no evidence at this time of higher insects such as flies, fleas, beetles, moths and butterflies, ants, bees and wasps.