The fungi are out in force right now, as are all the creatures that feed on them. This week I’ve been particularly drawn to puffballs.
Pear-shaped puffballs (Lycoperdon pyriforme).
On Wednesday I noticed a little wasp walking around on a gem-studded puffball (Lycoperdon perlatum). I don’t know what it is yet, but I assume it is a parasitoid of some other insect that feeds on fungi. I have been seeing a lot of parasitoid wasps wandering around on fungi lately, and at least a couple of times have seen them ovipositing into mushroom caps. [Added 11/1/11: Victor Kolyada has identified it as a Spilomicrus (Diapriidae). Diapriids parasitize a variety of flies, including vinegar flies (Drosophilidae), which are the main flies I have been seeing on fungi lately, and fungus gnats (Sciaroidea).]
Spilomicrus (Diapriidae; 1.5 mm) on the surface of a gem-studded puffball (Lycoperdon perlatum).
Because this little wasp had me looking extra closely at this particular pair of puffballs, I noticed that something seemed odd about the hole at the top of each one. They were neat little compact holes, not messily blown-open holes as I would expect from a ripe puffball releasing its spores. Also, the hole on one of the puffballs was noticeably off-center.
The hole at the top of the same puffball shown above.
Compare this with the more ragged hole in one of the puffballs shown at the top of this post:
The hole at the top of a pear-shaped puffball.
Of course, this isn’t an ideal comparison because these are two different kinds of puffballs, but the point is that something seemed odd to me about the gem-studded puffballs. So I tore open the one with the conspicuously off-center hole, and I found a mating pair of beetles inside. Here is one of them; like the slime mold beetles he is all dusty with spores:
One of a pair of handsome fungus beetles (Endomychidae; 5 mm) found inside a gem-studded puffball.
Brad Barnd on BugGuide.net identified this as a member of the family Endomychidae, known as the “handsome fungus beetles.” This beetle may not seem particularly handsome, but compare it with the forked fungus beetles shown in my last post. Also, I think the family gets its name more from species such as these:
Mycetina perpulchra, another handsome fungus beetle.
Endomychus biguttatus, another handsome fungus beetle.
I think the puffball beetle will turn out to be Lycoperdina ferruginea, both because it looks similar (to my eye) and because this is the only genus of endomychid known to feed on Lycoperdon puffballs*. The genus is clearly named for the association with puffballs. L. ferruginea is the only North American species. Here is a clean one photographed by Tom Murray.
Full disclosure: I didn’t take a picture of the hole in the puffball with the beetles in it before I tore it open. I found nothing inside the puffball that was right next to it, so I can’t say with absolute certainty that the hole in the gem-studded puffball shown above was made by one of these beetles. I haven’t found any more gem-studded puffballs since then to compare, and I’ve torn open a number of pear-shaped puffballs (Lycoperdon pyriforme) without finding anything inside. Except, that is, for this springtail that wandered out of the wreckage of one of them:
Orchesella celsa (Entomobryidae), a springtail that was apparently feeding inside a puffball.
And speaking of springtails, there is one visible in the photo at the top of this post, munching away at one of the pear-shaped puffballs. Can you spot it? Here is a closer look:
Ptenothrix marmorata (Dicyrtomidae; 1.7 mm) munching on the surface of a pear-shaped puffball.
Ptenothrix marmorata is one of the fanciest springtails out there. I had only seen one in my life before today, but on today’s walk I saw several mushrooms that were absolutely covered with them.
Part of a congregation of Ptenothrix marmorata at the top of a mushroom's stalk (the cap had fallen off). The elongate-bodied one is a tomocerid with injured antennae.
BugTracks 
Outstanding. A whole new micro-habitat to explore!