Thursday, May 20, 2010

Still Raining

 Rain beetle with interesting orange-red combs on its antennae.

It's still raining gobs in May which is unusual for California.  I feel like I'm still in Florida with the gators and moss.  I'm not complaining.  To show my appreciation for this unusual supply of precipitation, I'll share some info on one of the less common rain critters before moving onto spring wildflowers.

In late March, I was mowing the tall grass in the farmyard in preparation for an Easter Sunday picnic with friends and neighbors.  I even took 3 days off work to get the first big mowing done.  I should have known better when the rain beetles started buzzing around my head as I got started.  I spent much of those 'vacation' days weed-whipping in the rain and then we had to sponsor the 'picnic' inside after all.  It was raining buckets (err, baskets?) on Easter and 3 vehicles got stuck in my supplemental parking area, an area I refer to as the pig pen - oops.

Rain beetles (Pleocoma spp.) emerge from their largely underground life during or immediately after rainfall or snowmelt.  The 30-some species are distributed in mountainous areas from southern Washington to Baja California, Mexico.  Some species fly with the first fall/winter rains while others are active mid-winter or early spring.  Female rain beetles release pheromones which attract the flying males to their burrow for mating.  The male adult only lives for a few days.  The female waits for the eggs to develop (sometimes months) and then lays the eggs at the bottom of her burrow.  Rain beetle grubs live underground eating roots, in some species for 8 to 13 years.  The adult beetles stick to the task of reproduction in their short above-ground or near-surface days; they don't even eat as their mouthparts are partially fused and their digestive system is blocked by a membrane.

Taking a long nap after the breeding business.

Now that I've read up on rain beetles, I am curious as to which species I am seeing.  Each species' distribution can be very limited.  As explained in Introduction to California Beetles, "The known modern distribution of these apparently ancient beetles is restricted by the flightless females and is more or less correlated to areas of land that have never been subjected to glaciation or inundation by inland seas during the last two or three million years."

A rain beetle showed up today on my doorstep.  Does that mean it is going to rain hard again?  Note to self:  although not subject to glaciation, no parking in the pig pen.  

Evening snow (Linanthus dichotomus)
Forgot the name of this Linanthus/Leptosiphon wildflower blooming on serpentine soil in early April.
  I promise I will look it up in my other field notebook next time I am in the office, but I've got to get up early to do the dishes. 

If you know or wish to speculate on which species of rain beetle this is, please comment on this post.

See Also:
Generic Guide to New World Scarab Beetles, Pleocomidae, Frank T. Hovore, University of Nebraska State Museum - Division of Entomology.

Introduction to California Beetles, Arthur V. Evansand James H. Hogue, Introduction to California Beetles, UC Press, 2004.


  1. I didn't see a response to this post but wanted to mention that the black beetle with orange antennae is a species of Siphidae - not Pleocoma.

    Also, some species of Pleocoma are commonly seen flying during the day in bright sunlight - before or after precipitaion.

  2. Thanks BugDude. I'll look up more info about Siphidae and maybe they will visit again next year so I can look closer and confirm.

  3. Welcome.

    I misspelled the other beetle family. I meant: Silphidae (left out the "L" in my initial comment).

    Check out this image I found:

    Best wishes, ...

  4. Did you ever find out what species your rain beetle is? Your photo of the black beetle with orange bulbs on the antennae looks exactly like the big black beetles that spent several days dropping out of nowhere onto our floor in our house in Western Oregon this past week (November). I searched the web but your photo is the only one I can find that looks like our beetles. Thanks for any info you have found.

  5. I just heard about rain beetles yesterday. Cool! As I was googling images, yours came up Cindy. The reason why I clicked is that yours was NOT like the other scarab body types. Yours looks an awful lot like a black burying beetle (Nicrophorus nigrita I found recently:


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