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METALLIC DARKLING BEETLES

TENEBRIONIDAE: STENOCHIINAE

T

he family Tenebrionidae are called darkling

beetles, and their scientific name is derived

from the Latin tenebra, meaning darkness or gloom.

Both names refer to their nocturnal habits and

highlight the somber colors of most species, which

are usually brown or black. However, the mainly

tropical subfamily Stenochiinae are a conspicuous

exception to this rule, not only being colorful, but in

some cases brightly iridescent in the colors of the

rainbow. Like most metallic beetles, and unlike the

majority of tenebrionids, these species are active

during daylight, and the coloration, as elsewhere

in the beetles, seems to be a thermoregulation

adaptation, since the metallic reflective colors

absorb heat at low light levels, such as at dawn and

dusk, but reflect off excess heat during the hottest

parts of the day. The reflection may also help to

break up the beetles’ outline by reflecting light,

shadow, and surrounding objects in the

environment, hiding the beetle from potential

predators. Like most other tenebrionid beetles,

stenochiines also secrete strong-smelling quinones

as a defense.

The largest genus in the subfamily

Stenochiinae is Strongylium, a group of

more than 1,400 brightly metallic tropical

species. Strongylium are elongate, parallel

sided, and can be found on the leaves

and branches of tropical trees. The

larvae bore in the dead wood of

branches and trunks, and the adults

browse on fungi and lichen, and can quite

frequently be collected using a beating tray.

subfamily

Tenebrionidae: Stenochiinae

known species

2,500+

distribution

Worldwide except Antarctica, but almost

all species are found in the humid tropics

and subtropics

habitat

Most species inhabit trees in wet

tropical forests

size

5–40 mm

diet

The larvae of most species feed in dead

wood or fungal fruiting bodies. Adults

browse algae and fungi on tree bark

notes

Some species of Strongylium, like the one

illustrated bottom right, show behavioral

mimicry of tiger beetles, which are fast and

difficult to catch, and also have a strong

TENEBRIONIDAE: STENOCHIINAE

left | Tetraphyllus A hemispherical stenochiine

on the bark of a forest tree in Singapore. These

beetles graze algae on tree bark.