Caterpillar

prolegs thoracic legs

Classification: Two suborders, Frenatae and Jugatae, differing chiefly in wing venation and the way the front and hind wings are kept together; Rs in the hind wing is unbranched in frenates, branched in jugates; frenates generally have a frenulum (see opp.), and jugates have a jugum (a fingerlike lobe at base of front wing). The suborder Frenatae is divided into a series of superfamilies, which are arranged in 2 groups, Macrolepidoptera (p. 222) and Microlepidoptera (p. 240). Butterflies and skippers, making up the frenate superfamilies Papilionoidea and Hesperioidea, have knobbed antennae and lack a frenulum; moths (rest of order) have antennae of various sorts, usually threadlike or plumose (only rarely slightly clubbed), and they generally have a frenulum. No. of species: World, 112,000; N. America, 11,000. Identification of Lepidoptera: The principal characters used in separating families of Lepidoptera are those of the wing venation; other characters include the presence or absence of a frenulum, the presence or absence of ocelli, and characters of the legs, mouth parts, and antennae. Many of these characters are difficult to see, and most beginners try to identify their specimens from pictures. This method may be satisfactory for butterflies if a good illustrated guide such as Klots's A Field Guide to the Butterflies is available, but not for most of the moths (which make up the bulk of the order). The identification of most Lepidoptera to family requires a knowledge of wing venation and other characters.

The wing venation in the Lepidoptera is relatively simple, and that of a generalized frenate is shown opposite. Veins indicated by dotted lines are atrophied or lost in many groups. Loss of the basal portion of M results in the formation of a large cell in the central basal part of the wing. This is the discal cell, and it provides a starting point in identifying the veins. Sc and the anal veins are always free of the discal cell in the front wing, and the branches of R, M, and Cu come off this cell. Ten veins come off the discal cell in the front wing (if all are present): Ri, R2, R3, R4, R5, Mi, M2, Ms, Cui, and Cu2. In the frenate hind wing the anal veins are always free of the discal cell; Sc may or may not be free of this cell; Sc and Ri always fuse in the hind wing, and Rs is unbranched. The veins in the frenate hind wing (if all are present) are Sc + Ri, Rs, Mi, M2, Ma, Cui, and Cu2, plus 3 anal veins behind the discal cell. The venational variations encountered involve the number of veins present, how they branch, and where particular veins rise. The frenulum (see opp.) is a bristle or group of bristles at the base of the front edge of the hind wing.

The wing venation in most Lepidoptera is obscured by scales, and it is often necessary to bleach or remove the scales to see the venation; if the scales are not too dense, the venation can sometimes be seen if there is a strong light behind the wing. A drop of alcohol on the wing often reveals the venation. When the alcohol evaporates the wing coloration is usually unchanged.

discal cell accessory cell

Costa (C) Subcosta (Sc) Radius (R) Cubitus (Cu frenulum

discal cell

Generalized wing venation of a frenate. Veins shown by dotted lines are often weak or absent.

discal cell

Subcosta ( Radius (R) Cubitus (Cu)

frenulum discal cell accessory cell

Generalized wing venation of a frenate. Veins shown by dotted lines are often weak or absent.

The best way to see the wing venation in a lepidopteran is to bleach the wings. The procedure for bleaching and mounting lepidopteran wings is as follows:

1. Carefully remove wings from one side of the body (include frenulum if one is present).

2. Dip wings in 95 percent alcohol for a few seconds.

3. Dip wings in a 10 percent solution of hydrochloric acid for a few seconds.

4. Place wings in Clorox; leave them there until color is removed (up to several minutes). If wings are slow in clearing, dip them in acid again and then return them to the Clorox.

5. Rinse wings in water to remove the Clorox.

6. Place wings on a slide (a 2 x 2-in. slide for most wings). This is done by floating wings in a dish and bringing the slide up from underneath. After wings are on the slide, center and orient them.

7. Allow wings to dry, then place another slide (of same size) on top of wings and bind slides together with binding tape. Place the slide label on the outside. The result is a permanent slide mount that can be studied under a microscope, or projected with a slide projector.

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