Wedge-shaped beetles

Overview

Ripiphorus is the largest genus of wedge-shaped beetles. There are about 70 Ripiphorus species worldwide, about 30 species in North America north of Mexico, and at least 2 species in Minnesota. There are a number of records of the genus in Minnesota, but none of those records have identified the species.

Ripiphorus occurs in the United States, in Mexico, in Ontario, Canada, and in Europe. Larvae are parasites of sweat bees and other bees, and eventually kill their host. Adults live only a few days and are found on flowers and other vegetation. Information about their lives, including dietary preferences, is fragmented. The genus is in need of revision.

Description

Ripiphorus beetles look more like wasps or flies than beetles. Adults are ⅛″ to 7 ⁄16″ (4 to 11 mm) in length.

The head is vertical and is strongly constricted behind the eyes. The neck is inserted in the first thoracic segment (prothorax). The upper surface (vertex) is distinctly elevated above the front (anterior) margin of the upper thoracic plate (pronotum). The pair of chewing structures of the mouth (mandibles) are prominent and bent inward. There are two small, black, oval, prominent, compound eyes and no simple eyes (ocelli). The eyes are situated on the side of the head leaving a broad upper face (frons). The antennae are inserted above the eyes on each side of the vertex. On the female they have ten or eleven segments and may have projections on one side of each segment (monoflabellate), both sides (biflabellate), or be simply deeply sawtoothed (serrate). On both sexes, there are no projections or teeth on the first two segments.

The pronotum is broad. It does not have a sharp lateral ridge or a distinct suture. It is as wide at the base as the abdomen. The base has a large lobe in the middle that covers the plate over the wing bases (scutellum). The scutellum is exposed when the insect bends down to feed.

The abdomen of the female is deeply curved at the end, so much that the ovipositor is directed forward. The hardened forewings (elytra) are very short, convex, and scale-like. They do not extend beyond the thorax. The hindwings are entirely exposed.

The legs are short. The last part of the leg (tarsus), corresponding to the foot, is black and has five segments. On the hind leg it has only four segments. The first and last tarsal segments on the hind leg are the longest, the third segment is the shortest. There is a pair of toothed claws at the end of each tarsus.