I recently spent an afternoon hiking around a naturalized area on Bowyer Farm to take pictures of pollinators. This gem in the crown of the Cincinnati Zoo and Botanical Garden (CZBG) is located in western Warren County. Notably, the Farm enhances environmental diversity by developing naturalized areas and ephemeral wetlands.

My primary photographic target was pollinators visiting goldenrods (Solidago spp.). The late-season bloom of these native plants is a boon to pollinators. However, blooms were significantly suppressed this season in parts of Ohio that experienced the historic drought. Fortunately, recent rains helped to support a modest goldenrod recovery on Bowyer Farm.

Among the plethora of pollinators working over the goldenrod blooms was a wide range of flies (order Diptera). Diptera is the second most important taxonomic order relative to the number of plant pollinators found in the order, just behind bees and wasps (Hymenoptera) and ahead of moths and butterflies (Lepidoptera).

The images below of a Greenbottle Fly (Lucilia sericata, family Calliphoridae) demonstrate why flies are such important pollinators. Many have lapping mouthparts meaning they must belly up to the flower parts to lap up nectar. Although they aren’t as hairy as bees, they still transport pollen, particularly the sticky pollen produced by goldenrods and many other plants that depend on insects for pollination.

Calliphorids (e.g., blow flies, greenbottles, bluebottles) also provide other valuable ecological services beyond plant pollination. They are part of the cleanup crew converting carrion and dung into nutrients that flow back into the soil. Without these flies, we could be up to our necks in … well, we won’t go there.

Indeed, I’ve long contended that signs labeling pollinator gardens as “butterfly gardens” should be replaced with “fly gardens.” However, for some odd reason, my campaign hasn’t gotten much traction.

Unfortunately, the number of pictures of flies in my photo-library of pollinators lags way behind images of butterflies and moths. I have about the same number of pictures of beetles visiting flowers as flies although Coleoptera is the fourth most important taxonomic order in the pollinator lineup.

The reason I have so few images of flies visiting flowers is that they are hard to photograph. They have great eyesight and they’re great fliers which is why we call them flies.

That’s why I was thrilled with successfully moving to within a few inches of a fly on goldenrod to snap a few pictures without spooking my quarry. I privately congratulated myself on my stealthy photo-prowess. However, as I peered through the lens, I noticed the fly’s movements were a bit jerky and its head was twisted in an unnatural way. Then I realized it was dead! A zombie fly?

Along Came a Spider

Tamping down an impulse to flee at the perceived sight of a zombie fly, I parted the flowers to reveal the fly was actually lunch for a Crab Spider (order Araneae, family Thomisidae). The spider's cryptic yellow coloration allowed it to blend perfectly with the yellow goldenrod flowers.

I tentatively identified the spider as the Northern Crab Spider (Mecaphesa asperata). Pictures posted online show this spider clad in a range of colors including the bright yellow colors shown in my images. Likewise, I’ve taken pictures of this crab spider in the past sporting different color motifs. Interestingly, those shots commonly showed the spiders feeding on flies drawn to goldenrod.

Some crab spiders, such as the Goldenrod Crab Spider (Misumena vatia) and the White-banded Crab Spider (Misumenoides formosipes) can change their colors from white to yellow to match background colors. It’s not a quick change as with cuttlefish, but research has shown that the ability to change colors enhances the spider’s success with capturing prey. However, I could find no references that indicated the northern crab spider has a color-morphing capability.

Crab spiders are so-named owing to their general appearance and behavior. They are slightly flattened like a crab, and their front two pairs of legs are much longer than their back pairs. At rest, they hold the elongated legs outstretched like a crab. They also commonly move sideways like a crab.

Crab spiders can produce silk, but they don’t use it to capture their prey. Instead, they ambush their prey by laying motionless until their prey comes within striking range of their long front legs. The spiders are commonly found among flowers leading many to be called “flower spiders,” or “flower crab spiders.”

Once they seize their prey, which is most often an insect, they sink their fang-like mouthparts called “chelicerae” through the insect’s exoskeleton to inject venom that quickly paralyzes their victim. The fast-acting venom plays a critical role by allowing the spiders to successfully seize and dispatch much larger prey, even prey such as bees that could mount a strong defense.

Along with the venom, crab spiders also inject digestive enzymes that turn the victim's innards into goo. Then they slurp an insect protein shake.

Crab spiders are also known to ingest pollen and nectar. Thus, the goldenrod flowers provide the spiders with meat and potato meals.

Ambushed Flies

I came across another “zombie fly” only a short distance from the crab spider’s lunch special. However, this time, the killer was a Jagged Ambush Bug (Phymata spp., family Reduviidae). Meat items for these tiny predators are most often pollinators; a reminder that Nature doesn’t play favorites.

I’m not certain of the species of jagged ambush bug that I photographed sucking the life out of a fly on Bowyer Farm. Color patterns are not a dependable identification feature because they vary greatly with each species. Also, research has suggested that the bugs may be capable of changing colors but not as dramatically as with some crab spiders. Ambush bugs that are yellow simply become more yellow. Regardless, the color of the bug that I photographed blended seamlessly with the goldenrod bloom.

Jagged ambush bugs are common in Ohio. The "jagged" part of their common name comes from the jagged edges of their bodies which helps to break up the outline of their bodies. They are further camouflaged by mottled markings that act like a tiger’s stripes allowing the bugs to blend with light and shadows.

Sometimes, the common names of insects not only describe what the insect looks like but also what the insect does for a living. Insects belonging to the Hemipteran family Reduviidae are called assassin bugs; they are killers. Assassin bugs that belong to the subfamily Phymatinae are called ambush bugs because they kill by surprise attack.

Ambush bugs remain motionless, sometimes for hours, lying in wait for their victims. They increase their chances of success by relying on the nectar and pollen of flowers to draw in their prey. Of course, this means they commonly dine on pollinators.

Ambush bugs seldom measure more than 1/2" in length. However, these small rapacious predators are equipped with dramatically outsized front legs designed to grab and hold their prey.

As with all assassin bugs, ambush bugs use their stiletto-like piercing-sucking mouthparts called a "proboscis" (= beak) to stab their victims and inject immobilizing paralytic chemicals along with digestive enzymes. As with the crab spider, the bug’s enzymes dissolve their victim's innards allowing the bugs to extract the essence of insect.

The table fare of these voracious ambush predators may include small bees, wasps, flies, and other flying insects intent on gathering pollen or grabbing a nectar snack. Few escape the embrace of the bug's raptorial front legs.

However, size matters. Last year, I watched an ambush bug continually trying and failing to snag European honey bees (Apis mellifera). The drama is captured in the following images.

You may find ambush bugs taking advantage of a wide range of flowers to attract an insect meal. As shown in images posted in this Alert, Late-Flowering Thoroughwort (Eupatorium serotinum, family Apiaceae (formerly Umbelliferae)) is a favorite because it’s such a pollinator magnet.

Earlier in the season, ambush bugs were commonly found on Queen Anne's lace (Daucus carota, family Apiaceae). The bugs love to conceal themselves just beneath the umbellifer flowers so they can pop up and grab an unsuspecting victim. I'm always amazed at how well the ambush bugs blend with the composite flowers.

Ron Wilson