Chalcid wasps in homes

After identifying an unusual insect for a homeowner today, the thank you email ended with a bang. Because I was able to quickly identify her pest, which her PMP had incorrectly insisted was a "bee", she concluded, "[I guess] it's best I change pest control companies."

Could you identify this insect from this picture? Brachymeria
podagrica is a chalcid wasp parasitoid that attacks filth flies,
like those that feed on carrion.

Ouch... I hate to hear that.

Admittedly the insect was an obscure critter. I'm guessing that not one in 100 PMPs has ever heard of a chalcid (CHAL sid) wasp before. But chalcid wasps are common natural enemies of many insect pests. Identified by their small size and giant hind femurs, the Chalcididae family makes up one of the dozen or so "parasitoid" wasp families within the bee/wasp/ant order Hymenoptera.

Parasitoid wasps are certainly one of the most fascinating and wonderful, yet horrifying, of all creatures.  So seemingly cruel in its behavior that theologians and biologists argued over the last 200 years whether the mere existence of insects like the ichneumon wasp (a cousin of the chalcid wasp) served as proof against the Christian belief in a loving Creator-God.*

Parasitoids are parasite-like predators. Like a parasite, they grow up feeding on or in a single host. But unlike true parasites, which weaken but rarely kill, parasitoids invariably kill their hosts. Parasitoids begin their lives as an egg laid by their mother on a soft part of a host's anatomy. Upon hatching the parasitoid larva burrows into the body cavity of its host and begins feeding. The larva knows instinctively to begin with the non-essential parts, prolonging the life of its victim as long as possible. Eaten alive from the inside, ultimately the host dies. Ugh.

It does sound cruel, but parasitoids are also one of nature's most effective population control agents. Without them, crops would vanish under billions of caterpillars.  Flies would breed unchecked. Even spiders would be more abundant than they already are.  Parasitoid wasps possess some of the world's sharpest "noses" (actually antennae), able to sniff out prey even when the prey are vanishingly rare. They are also smart, with some species recently being trained to sniff out illicit drugs and even bombs on the battlefield. Gardeners and farmers, especially, reap the benefits of parasitoid services every day.

The key to identifying chalcid wasps is their tiny size (this is one 
of  the larger chalcids at 5 mm), reduced veination in the wings, 
and swollen hind femurs. This Brachymeria podagrica is further 
identified by its distinctive markings. Photo courtesy Graham
Montgomery via Bugguide.net.

Admittedly we in structural pest control don't have many chances to encounter parasitic insects in our daily work.  Most parasitoid wasps live peacefully out of sight in the natural world, ill at ease in our indoor environments. Occasionally, though, parasitoid wasps make an appearance in a home or business. For this reason, it's a good idea for PMPs to know something about these insects.

The species of chalcid wasp my homeowner encountered "swarming" in her attic this spring appeared identical to other similar wasp pictures I've received recently.  These turned out to be Brachymeria podagrica, a parasitoid (primarily) of flies.  Their presence indoors suggests that the source could have been a dead animal full of fly larvae somewhere in the home--a theory backed up in this case by the homeowner's report of a foul stench several days before the little wasps appeared in the attic. Likely they were drawn to the smell of the carcass in search of their blow fly hosts.

When one, or a few, unusual insects show up overnight in a structure, they are often called "accidental invaders". Accidental invaders are chance occurrences, when an insect or spider accidentally enters through an open door or window, or unsealed crack. Such accidental entries occur on a regular basis in residential accounts, but usually with a variety of arthropods.  But when several (or dozens) of the same kind of insect appear inside a home, or when the same insects show up over many days, it usually means something is afoot. Insects always have a story to tell, and they never lie.

Chalcid wasps are not likely to enter an account over and over by accident. If you find chalcids indoors, get a sample and have them identified. Brachymeria podagrica suggests the possibility of wildlife or rodents; however other species of Brachymeria and other species of chalcids are known to parasitize beetle or moth larvae, and might be evidence of a stored product pest infestation.

And remember, if you're ever unsure of the identification of an insect, don't hesitate to bring it to your in-house entomologist (if you have one), or send to your state university or other reputable insect ID authority. And don't just call something strange a "bee" unless you know for sure that it is.

* An interesting discussion of the ichneumon wasp controversy can be found in Stephen Jay Gould's essay on Non-moral Nature in the book Hen's Teeth and Horse's Toes. 

An odd "pest"

Even when not an insect, if an object is small and mysterious, it will often be called a "bug" and end up on the desk of an entomologist.  Such was the case with some specimens I received last week.  They were described by a pest management professional as "tiny bugs" that appeared on the south side of a customer's house every year.  No mulch or trees or shrubs were reported nearby.

I thought at first that these tiny (1.3 mm length) objects might be spores from the artillery fungus, in the genus Sphaerobolus.  Artillery, or shotgun, fungus is a type of primitive plant that grows as a saprophyte on wood mulch.  It has tiny black spores that it can shoot for several yards.  The spores are sticky and adhere to a variety of surfaces, like walls of homes, sometimes leaving a stain when removed.  But, according to the submitter there was no mulch nearby, and according to my plant pathologist friend, Dr. Kevin Ong, the specimen I was looking at under my microscope was not smoothly round as typical for Sphaerobolus.  

These tiny, 1.3 mm, seeds from the Oxalis plant are sometimes
ejected from the plant and stick to man-made surfaces, like
exterior walls, where they may be confused with "bugs".

My sample of 20 or so objects were teardrop-shaped and ridged/segmented.  Under the microscope they looked vaguely insect-like but appeared to lack legs and mouthparts.  Fortunately I network with many experienced entomologists around the country, several of whom kindly informed me that the sample was actually the seed of Oxalis, a common garden weed or plant.

One entomologist who wrote back noted that he once got a series of calls from a commercial greenhouse grower who was doing his best to "kill" these "pests" "crawling" all over his greenhouse, but with little success.  This is another example of why it is so important to identify the pest before reaching for the insecticide sprayer.

As it turns out, Oxalis seeds are pretty cool.  They are borne by the plant in a cylindrical pod.  When mature, or when the rip seed pod is touched, it shoots out the small seeds three to five feet.  The rough coats on the seeds helps them stick to some surfaces (like a hardy-board exterior wall, in this case). For a good video showing how Oxalis seed dispersal works, check this out.  The plants themselves are attractive, if sometimes difficult to eradicate from your yard.  The plant leaves are sour-tasting because of the presence of oxalic acid; but in small quantities are good in salads.

So let's not be quick to blame insects for those strange objects that customers are prone to find around the home.  If you don't know what something is, have it checked out by me (if you're in Texas) or one of the other fine entomologists most states (and many pest control companies) are blessed with.  There are enough real insects in the world to keep all of us entomologists busy full-time.

No such thing as an "ant"!

I'm convinced that training employees to document what they do is one of the most important, yet overlooked, aspects of technician training in pest control. If you're doing your work well, you want your work documented in the service tickets and logs and other paperwork you leave behind.

One of the best indicators of a well-trained technician is careful and descriptive recording of pest problems encountered during a service visit. One of the signs of a careless or poorly trained technician is sloppy notes.

I first noticed this a few years ago when serving as an expert in lawsuits involving fire ant stinging accidents in nursing homes. As part of the discovery process, it was my job to go through service tickets and note when and where fire ants had been noted by the pest control company.

To my dismay, I found that there was no way to distinguish what the technicians had been doing during their many visits to the locations I researched. Notations on the service logs and service tickets would typically read "treated for ants". Wait a minute. There's no such thing as just an 'ant'. What kind of ants? Pharaoh ants would require applying one of a few effective protein-based baits designed for pharaoh ants. Odorous house ants might require a sugar-based bait. For fire ants an outdoor treatment and inspection would be necessary, along with use of broadcast fire ant baits or outdoor mound treatments. Without good documentation, one has to assume that the technician didn't really know (or care) what he was doing.

We encounter the same problem when reviewing service tickets left behind in public schools. The past few years my colleague Janet Hurley and I have visited a number of public schools in various states to audit their IPM programs. In the process we've seen many service tickets left behind by pest control technicians documenting pesticide applications for "ants", "roaches", "flies", etc. As anyone who has worked in the industry can tell you, identifying a potential pest to ordinal level doesn't really tell you much. There's a world of difference, for example, between finding a dozen German cockroach nymphs and an American cockroach in a sticky card in a previously cockroach-free commercial kitchen. Think potentially dozens of service hours and repeated callbacks if the problem is not caught early. There's no such thing as just a "roach".

Flies are another great example of why identification skills and documentation are so important. Fly control is based on finding and eliminating the site where the larval stages of the flies are breeding. House flies in a kitchen? Check the outdoor dumpster and the back door. Fruit flies typically involve spilled syrups, rotten fruits or vegetables. Phorid flies may indicate a sewer problem. The customer may not know the difference, but the technician should. And the technician should communicate with the customer, a process that starts with the service ticket. There's no such thing a just a "fly".

Documenting pesticide use is another issue that I will undoubtedly revisit on another day. But today, just remember that when it comes to quality pest control, "there's no such thing as an 'ant'!"