Killers in a North Florida Garden (Another predator story)

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This past weekend, many of us stared at our flowers for the Great Southeast Pollinator Census. We saw bees and butterflies, of course. Maybe you added a few ticks in the “Flies” or “Wasps” boxes. Did anyone see “Other Insects?” What I want to know, more than anything else, is whether anyone saw their pollinators devoured by those other insects. Or a spider. Or, perhaps, devoured by another pollinator.

If you’ve clicked on pollinator content on the WFSU Ecology Blog before, you might wonder, “What is this guy’s obsession with insects (and spiders) eating each other?” What a ghoul! Yes, I’ve written about predators eating caterpillars, mostly, and then there’s that one where a wasp ate a butterfly as she was mating (the male was unfazed by this development).

I started writing about garden predators when about twenty or so monarch caterpillars disappeared from my yard overnight. That led me to look more closely at the other insects on my milkweed plants. It also led me to do some research. A little knowledge made me feel better about caterpillars being eaten. A little more knowledge, and more observation, led to a change in how I saw my garden.

Most of us build native plant gardens to attract pollinators, this category of insect that needs our help. They need our help, and our help comes in the form of attractive wildflower, leading to aesthetically pleasing butterflies doing magical things like posing majestically while they eat, or leaving caterpillars on our plants to eat and grow and make chrysalises.

But, what if our garden’s greatest contribution to the environment is protein for the food web?

Fueling the backyard food web

Well, of course insects are more than just food. They are decomposers, plant consumers, parasites, and predators. They often check more than one box in our human-imposed categories list. Insects lead two lives, their larval life and their adult life. It’s not quite the life of human children and adults. Some insect larvae are hunters. Mayfly larvae spend a year in the muck at the bottom of a waterway, and their adult life is two days of flying and mating. Most bees and wasps are fed by their mothers, while moths and butterflies lay eggs and fly away.

As I research the insects I see on my flowers, I find that many have relationships with other insects in my yard. Many of these associations are tied to reproduction. There are insects who hunt to feed their larvae, and those who hunt for themselves. Many insects are only in your yard because they eat or parasitize some other specific insect in your yard. The more robust your backyard ecosystem, the more of these relationships there are. Sometimes, we can see these relationships play out in a violent way. Most of the time, I see an insect, read about it, and learn about unseen interactions.

My interest in these interactions are not driven by bloodlust as much as uncovering the inner workings of a functioning ecosystem. The garden is a harsher place than we might expect. But it is a dynamic place.

My goal here, as with other insect predator posts, is to get folks familiar with those insects we weren’t thinking about when we planted coneflowers in our garden beds. These uninvited insects can be freaky. They may eat the insects you were hoping to attract. But, they are as much an indicator of garden health as bees and butterflies.

Classic Beneficial Insects

I’m going to start with a few of the predators we call “Beneficial Insects.” It’s not my favorite way of thinking about insects. We say beneficial because we’re thinking about plant health. These insects eat the insects eating your plants. Sometimes we want our ornamentals and food plants left alone. If we’re creating a habitat with native plants, though, we expect that many insects will feed on them. We buy some plants specifically to be eaten – though I did recently meet someone who asked me if monarchs ate anything other than milkweed, because she wanted them to not eat her milkweed.

I was surprised by the question, but it says a lot about how we view insects. Their value to us is tied to the vision we have for our outdoor spaces. The beneficial/ pest labels say more about how we feel about insects than their value in an ecosystem.

Ladybugs (Also known as lady beetles)

This family of beetle (Coccinellidae) is among the most recognizable of garden predators. Both adults and larvae feed on small, plant-eating insects.

According to UF/IFAS (Institute of Food and Agricultural Sciences), there are 98 species of lady beetle in Florida. And yet, the one we are increasingly likely to see in the garden is the invasive Asian lady beetle. The Asian lady beetle occupies a similar niche as native ladybugs, but not all 98 ladybug species in Florida do the exact same thing. When Asian lady beetles displace the native species, something gets lost. And they displace them in a most aggressive way.

One day I went to check on ladybug eggs I had spotted on some Spanish moss hanging from our pecan tree. When I saw the scene above, my first thought was that I was witnessing some motherly love. But, that’s not the way most insects parent. Asian lady beetles eat the larvae of competitor lady beetles.

I don’t usually like these labels, but an Asian lady beetle is a pest with aspects of a beneficial insect. It does eat and help regulate plant-eating insects, but by reducing the diversity of lady beetle species, it leaves some niches unfilled. One species isn’t going to eat all of the things that 98 species eat, in all of the places they eat them.

Assassin bugs

A classic garden enforcer. It ambushes plant-eating insects, inserts its long proboscis, and sucks the life out of them. The one I most often see in my yard is the milkweed assassin. The name comes from its red and black color scheme, which resembles milkweed bugs and milkweed beetles. It is not an insect with any preference for milkweed or monarch caterpillars, though.

I’ve also seen this one in the yard:

Hoverflies (also known as Syrphid Flies)

What’s not to like about hoverflies? As larvae, they hunt and eat aphids, and as adults, they are bee-mimic pollinators. They can be easy to miss in the garden, as they are small and often visit small flowers.

The easiest place to spot them is on or near an aphid-covered plant. Milkweed is a plant with its own specialist aphid, the milkweed aphid, which can become plentiful on flowers and seed pods. Watching milkweed plants as often as I do, I tend to see more of hoverfly larvae than I do adults.

I first noticed syrphid larvae on plants from which monarch caterpillars disappeared. They have been observed eating smaller caterpillars, which are soft-bodied creatures not too much larger than their typical prey. Caterpillars are at their most vulnerable in their first instar phase, after they hatch from an egg.

The larvae are not as cute as the adults, but they do good work.

Lacewings

Lacewing larvae are also aphid predators, and are often used as pest control. They, too, eat monarch caterpillars and eggs.

One morning, I saw a telltale small hole on a milkweed leaf, and found a couple of small caterpillars. On another part of the plant, I also found a lacewing larva. There was a time when I would have interfered, and moved the small caterpillars to another plant, or into an enclosure. I no longer do that. The research is on the side of letting natural selection play out; the species benefits from it even if individuals do not.

I did not find caterpillars when I checked the following day.

Wasps

Now, to a less well-liked group of insects.

The WFSU Ecology Blog has a whole page dedicated to wasp species I’ve photographed in north Florida. I don’t need to republish that whole page here. The thing to understand about them is that, as adults they are pollinators. Their larvae eat meat though, and to feed them, parents are also hunters.

They are not only hunters, they are specialists. Every species of wasp has an insect (or spider) they are looking for. The species I most often see hunting are going after caterpillars in the yard.

Every time I see a new wasp, I look it up. Bugguide.net usually has information on prey species for wasps, host plants for moth and butterfly caterpillars, and hosts for parasitic species. If it’s not listed under the specific species, you can navigate up to the genus or other higher taxon. For instance, the family Scoliidae (scoliid wasps) parasitize scarab beetle larvae and bring them back to their nests. These larvae are typically below ground, and so this is action I’m not likely to witness.

For other wasps species, their common names tell you what you need to know.

We have wasps hunting stink bugs and leaf-footed bugs, and others hunting cicadas. The digger wasps visiting my horsemint at this time of year hunt grasshoppers and crickets. All of these wasps are eating plant consumers, keeping them in check. I see them in my yard because I have wildflowers to feed them, and plenty of other insects to feed their larvae.

Not all wasps are hunting plant eaters:

Parasitic wasps

Let’s take a look at the wasp below. That needle-like structure protruding from its abdomen is not a stinger, though this wasp will inflict some pain with it. This needle is the ovipositor, the means by which it injects eggs into a host insect.

This is a parasitic wasp in the family Braconidae. Braconidae and the family Ichneumonidae are the two largest families of wasps, bees, or ants (the order Hymenoptera), and both families are parasitic breeders. They inject eggs into prey species along with a chemical cocktail. One chemical subdues the prey temporarily, while others turn off immune responses that would harm a parasite. Some species of parasitoid wasps arrest the development of larval species so that don’t metamorphose and possibly harm the larvae inside them. Other parasitoids don’t mature until after the host makes a chrysalis.

The best known braconid is the hornworm parasitoid wasp (Cotesia congregata). You may have seen a photo of a tobacco hornworm, those famous tomato plant eaters, with white nodes growing out of them. Parasitoid wasps are another check on plant consuming insects.

Robber flies

One of my favorite types of insect eats another of my favorites. I don’t like seeing robber flies eating bees, but these are some fearsome predators. And I can’t help but admire the bee-mimic robber flies, using a disguise that helps them get close to bees.

Many of them specialize in bees, and some eat other robber fly species, actually. But many others also help check plant consuming species. Some robber flies are quite large:

Other flies

We’ve already talked about hoverflies and robber flies. There are a couple of other killer flies I wanted to highlight, cool-looking insects I found pollinating flowers.

This is a parasitic breeder, and it is known to parasitize bumblebees. Physocephala sagittaria will tackle bumblebees while in flight, and inject them with eggs. The larvae will then will devour them from within. Another bee-killer, and I do love the bees. The only time I’ve spotted this fly in the yard was later in the fall, when common eastern bumblebee workers had become plentiful in the yard.

Below are a couple of Tachinid flies, which are also parasites.

These flies are both in the genus Trichopoda. The one on the left parasitizes leaf-footed bugs, while the one on the right parasitizes stinkbugs. These insects help control plant consumers. But then, some stinkbugs are also predators:

Kleptoparasites

We have already seen a few predators that will eat or parasitize bees. Sometimes the insect killing a bee is another bee. Not an adult bee killing an adult bee, but a larva killing a larva or egg. Thirteen percent of bees are kleptoparasites, or cuckoo bees.

Female kleptoparasites collect no pollen and build no nests. Instead, they fly into the nest of another bee while the mother is out collecting pollen, and lay eggs at the wall of a brood cell. In their first instar phase, kleptoparasitic bee larvae have large mandibles. They use these to kill the host egg and eat the pollen left for it.

Sharp-tailed bees specialize in leafcutter bees in the genus Megachile. They use their sharp “tails” to puncture the wall of a brood cell, and deposits an egg on the edge of it. A minuscule larva then swims across the pollen to the egg at the center, which it kills.

Bees in the genus Triepeolus specialize in longhorn bees. I wrote a post last fall about another species of longhorn-cuckoo in a large aggregation of sandhill longhorn bees.

Cuckoo bees are typically shaped like wasps, and the tips of their abdomens (their ovipositors) are pointed. They have a tougher skin than most bees, since they are likely to be attacked. And they are never far from their host bee species.

Some bee kleptoparasites are not bees. Tiger bee flies are never far from carpenter bees nests. They lay eggs near the opening, and their larvae crawl in to take the pollen. Other bee flies are parasites or kleptoparasites of other insects.

Green lynx spiders

And now, finally, a spider.

I could add plenty of images of insects in spiderwebs, but we’ve all seen that. I do want to highlight one spider, since this post has a little bit of a pollinator focus. Green lynx spiders ambush predators on wildflowers, sometimes lying translucently on top of them.

There are so many predators eating our pollinators, and I haven’t even gotten into vertebrates. Birds, lizards, frogs, and all the rest feast on our insects. And that’s okay. The insect declines we read about aren’t caused by insect predators, they’re caused by habitat loss and land management. If you have a lot of insects eating each other, you have a lot of insects. And you might just have a healthy habitat.

You can’t rescue every bumblebee and monarch caterpillar from a predator. But if you plant native plants, and include habitat features like decomposing wood and bare patches of soil, you create a space for these dramas to play out. And when you see it playing out, or learn about the players, you begin to reveal the threads of the web holding it all together. One connection leads to another. If you’re lucky, you will keep finding new connections in your garden space, and continue to gain a deeper understanding of your backyard ecosystem.