More Black And Yellow Peculiarities cont.

Rodney S. Hanley rshanley at FALCON.CC.UKANS.EDU
Fri Jan 23 09:22:56 CST 1998

Thomas Schlemmermeyer wrote:

"This time a supposed terrestrian animal came very near to the water.
During my stays at Boraceia/Atlantic Rain Forest I observed beetles of
the family "Sandlaufkaefer" (Is it Scarabeidae? Sorry, I'm bad in beetle
systematics.) They were so suspicious, as they had a large yellow point
on each elytrum. And they were running in the water beds of the many
small rivers rapidly on the moistened rocks in the zone where algae are
growing but which might be judged still terrestrian.

>From time to time they made small flights to change from one rock to the
other.  I suppose that they are highly seasonal as I never observed them
before. And it is my first stay in Boraceia in january.

OK, I admit that there are more than just a few beetle species in the
world. But if my description makes any sense or allusion to known facts,
it would be great to hear."

Thomas (and other interested Taxacomers):

It is quite likely that the beetles you referred to are members of the
genus Stenus (Coleoptera: Staphylinidae: Steninae).  There are about 200
species in the subfamily throughout the world, with most 3-5mm long.
These critters are well known "water skaters" that are rather elongate
with large bulging eyes.  Typically, they occur in sunny spots along
muddy or sandy shores of lakes, ponds, and streams.  All known species
are carnivorous.  One very interesting tid-bit is that these beetles
secrete a chemical from the tip of their abdomen that breaks the surface
tension of the water when threatened.  This behavior has the effect of
"scooting" the beetle across the surface of the water to safety.  Sort
of a natural jet propulsion.


---Rod Hanley

Snow Entomological Museum
Snow Hall
University of Kansas
Lawrence, Kansas  66045  USA

E-mail:  rshanley at

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