Family: Ptinidae (spider beetles)

Life > Eukaryotes > Opisthokonta > Metazoa (animals) > Bilateria > Ecdysozoa > Panarthropoda > Tritocerebra > Arthopoda > Mandibulata > Atelocerata > Panhexapoda > Hexapoda > Insecta (insects) > Dicondyla > Pterygota > Metapterygota > Neoptera > Eumetabola > Holometabola > Coleoptera (beetles) > Polyphaga > Superfamily: Bostrychoidea

Small (2-5mm), spider-like beetles with rounded, globular bodies and long legs. The head is obscured from above by the pronotum. They are scavengers and feed on dry animal and vegetable matter and are found in birds' , animal nests and caves.

Mezium americanum, American spider beetle.  [image H. Robertson, Iziko ©].

The American spider beetle is found throughout the world and is a pest of stored products such as grains and cayenne pepper. The smooth shiny elytra, the dense mat of hairs on the pronotum as well as the interrupted (scalloped) line of dense hairs at the base of the elytra make it easy to identify. There is a closely related stored product pest called the Northern spider beetle Mezium affine but it is evidently only found in the Northern Hemisphere. It is similar in appearance to M. americanum but is distinguished from it in having a continuous line of dense hairs at the base of the elytra (not scalloped).

If you encounter large numbers of these beetles in your home it probably means there is an old bag of dried food in a cupboard somewhere in which this beetle is breeding. Clearing out the infested food will solve the problem although you need to watch out in case the beetles have started laying their eggs in other exposed food nearby. Sealing of dried foods in plastic containers would have prevented the problem in the first place.

Page by Margie Cochrane