Today we’re going to briefly discuss the identification of insects that aren’t adults yet.
I. Incomplete metamorphosis
Immature insects are not always easy to identify. For example, what were our red mystery insects last week?
Zooming in we can see this bug has its proboscis, or straw-like mouthparts, stuck into the plant. It is a true bug. In fact, as Sara pointed out, these red bugs are the nymphs of milkweed bugs.
You can tell they are not adults because of the short, dark pads where the wings would be. Only adult insects have wings. Insects that don’t change drastically in shape between molts, or insects with incomplete metamorphosis, have a series of stages called nymphs.
In this case the nymphs are likely to be small milkweed bugs, Lygaeus kalmaii, which are the most common kinds in our yard. Notice the two white spots on the black part of the wings of this adult.
How can we know for sure which bugs the nymphs will turn into? One way is to have patience and wait until they become adults. Adults are much easier to identify via field guides.
The nymphs may be different colors than the adult. That stripy-legged youngster is the nymph of an assassin bug.
An adult assassin bug lacks the stripes. However, you can still recognize the overall shape.
The nymphs in this cluster have just hatched out of their eggs. These are shield bug nymphs. Once again, the insects lack wings (see adult shield bug)
Other groups that have nymphs include cicadas, like the one above. Cicada nymphs may live for years under the ground.
Grasshoppers also have nymphs, as do aphids, leafhoppers, praying mantids and cockroaches, among others.
II. Complete metamorphosis
A. Lepidoptera
Although many of us recognize the life stages of a butterfly, some of the life stages of other orders with complete metamorphosis can be tricky.
Ever found one of these in the soil? Do you know what it is? It is the pupal stage of a moth (see post about moth life cycles)
B. Coleoptera
What about these orange and black insects? The insects in the photographs above turn into lady beetles, similar to this one:
Most of us recognize that adult lady beetles are beneficial insects. The youngsters are beneficial as well (more about lady beetle life cycles).
Some beetle larvae look more like worms or caterpillars. This video has a nice summary of the life cycle of darkling beetles (its larvae are called mealworms).
c. Hymenoptera
What are the “grubs” in this photograph? Those are sweat bee larvae (more photographs of the sweat bee life cycle at Wild About Ants).
Ants also have eggs, larvae and pupae, sometimes in cocoons (graphic from Wild About Ants)
Unfortunately, we only have space for a brief introduction to immature insect and life cycles here.
Where can you get further help identifying immature insects?
A classic book, How to Know the Immature Insects by H.F. Chu (1949) is available online or for download at Biodiversity Heritage Library. It is a key with black and white line drawings, and requires some knowledge of entomological terminology.
BugGuide.net is a wonderful resource. It may take a bit of persistence, but they have photographs of many, many insects, often identified to species. Click on the insect that most resembles yours in the left sidebar and then keep going. Try the images tab as well.
Insect Identification.org is a bit easier to use, but does have large ads
Here at Growing with Science we have posts about how to recognize the 5 major orders of insects, as well as the Bug of the Week archive.
Have you ever been mystified by an immature insect? What did it turn out to be?
For example, would you know this larva would turn into a beetle?
Although the head capsule may look a bit like a caterpillar, this is a beetle larva commonly called a white grub. It lives in the soil and will turn into a type of scarab beetles called a “June beetle.”
Turning it over, it has two dark spots, which are the developing eyes. This is the pupal stage of a seed beetle or bruchid.
