Monday, June 11, 2012

Narrow Searcher

This large shiny black beetle is called a Narrow Searcher (Calosoma externum). They are found throughout Eastern North America near deciduous woodlands. They are often referred to as caterpillar hunters or searchers, which hints at their preferred food choices. They often prey on the caterpillars of a wide variety of moths and butterflies. They will however feed on other inverts as well. They are capable of producing a terrible smelling fluid from glands at the end of their abdomen, which they will spray at potential predators as a form of defense. It is often found in woodlands, grasslands, disturbed lands, river bottoms and near cropland. They typically hunt or "search" for potential prey insects on the ground, but they will occasionally climb trees in search of food. Because of their preference for eating potentially harmful caterpillars they are considered beneficial to both the gardener and farmer.

These are large beetles measuring up to35 mm in length. Their body is black with brilliant bluish-purple margins. Their elytra (wings) are grooved. This beetle is incredibly fast moving and difficult to capture. They often hide under rock or log piles during the day and come out at night to search for food. It is common to find them at lights at night, presumably these are the opportunistic hunters.
The adults of this species overwinter in the ground and emerge when spring returns. At this time they will seek mates.

Because of the voracious appetite this genus has for insects and especially caterpillars, one species was imported; Calosoma sycophanta was brought into the United States in 1905 as a form of biological control against the Gypsy Moth.This species originated in Europe and seems to have a particular fondness for caterpillars.

The Narrow Searcher is a native species and can be found throughout much of the United States. I frequently find them in our implement sheds where they are probably seeking the many insects that seem to live inside the buildings. It is always exciting to find such a large, quick moving beetle.


  1. I just found a beautiful, bright green it the same? (I live in illinois)