Zelus longipes aka the Milkweed Assassin Bug is perhaps my favorite insect to see in the garden. It should be one of yours too! Closely related to Wheel Bugs, assassin bugs are a great predatory insect that help keep balance in every garden's ecosystem. They eat almost every destructive critter that most gardeners are pulling their hair out to eliminate. Some of the assassin bug's favorite targets:
As you might guess, they don't eat ONLY the bad bugs. So unfortunately, assassin bugs will prey on the caterpillars we enjoy seeing in the garden such as monarchs, queens, zebra longwings, and so on. They also prey on ladybeetle and lacewing larvae which prey on aphids. And even small bees and flies that serve as beneficial pollinators. But it's a bug eat bug world out there. The assassin bug is one of the most beneficial predators in a vegetable garden since it targets some of the most destructive pests. This is nature's pesticide.
Adult Milkweed Assassin Bug Z. longipes on Pink Swamp Milkweed Asclepias incarnata. Photo by FOL taken in The Serene Forest
Milkweed Assassin Bugs are typically easy to pick out in the garden. They do have a few look-alike bugs such as the Milkweed Bug, and the nymphs of the Eastern Leaffooted Bug. But generally adults stand out with their long bodied, orange and black color, black wings, long legs, long antennae, pear shaped head, and beak. The orange and black color is specific to North American Milkweed Assassin Bugs.
Nymphs look very similar to nymphs of the Eastern Leaffooted Bug. The biggest distinguishing characteristics are the lack of raised black dots on the Assassin Bug nymphs. In fact, nymphs are usually entirely orange with the exception of their black legs. The legs are long in proportion to their bodies giving them a second common name "Longlegged Assassin Bug". The long legs can make the nymphs seem like bright orange spiders.
Eggs are cylindirical in shape and have a brown color. Female assassin bugs typically will lay their eggs in a cluster on the underside of leaves. There is not technically a host plant for these insects unlike most other garden critters. Instead, female assassing bugs will lay eggs in areas that are most likely going to provide easy meals for the brand new instars. Leaves of plants that attract caterpillars are generally where eggs will be laid. For example, corn leaves, cabbage leaves, milkweed leaves, etc. Young caterpillars and other soft insects make an easier meal for young instars.
Mature assassin bugs can fly throughout the garden hunting down perfect locations to ambush their prey. They use their front legs like a glue trap. A viscous liquid is secreted and they will lie in wait with the forelegs raised up high until their unsuspecting target is close enough. Once trapped, the prey becomes paralyzed as the assassin bug inserts its stylet inside the prey's body. Afterwards, it reinserts the sylet into the prey to be used like a straw. Digestive enzymes are then pushed inside the prey that begin breaking down tissue into a soft absorbable liquid that is later sucked back out. Assassin bugs have been observed ambushing and feeding on prey up to 6x their size.
Adult Milkweed Assassin Bug feeding on the caterpillar of a Zebra Longwing. Photo taken by FOL in The Serene Forest
In this picture you can see that the assassin bug hid under this corky stem passionvine leaf until this zebra longwing caterpillar got close enough to the edge. The assassin bug has inserted the stylet and has begun its process of extra-oral digestion. While we hate to see a zebra longwing caterpillar fall to a predator, remember that the garden is a constant battle of balance. The next captured prey may be something competing for vegetables or other crops.
One final note about Milkweed Assassin Bugs. Please do not attempt to handle them without gloves on. They are not aggressive, nor do they want to bite humans. But, a bite from one of these critters can be painful and cause localized swelling.
Have you had any experiences with assassin bugs? Keep the conversation going by commenting below.