How to Identify Dytiscids(diving beetles) from Hydrophilids(water scavenger beetles)!

  

Just by looking at these two images, can you tell what family each one belongs to? These two insects look quite similar, but if you know what to look for, you shall be able to tell which one is which. The first image is that of a Dytiscid(predacious diving beetle), and the second a Hydrophilid(water scavenger beetle). Here is how to tell them apart by appearance: 
Dytiscids have a rounded ventral(under) side, while Hydrophilids have flat ones. Flipping the insects totally over onto the ventral sides, you may notice that Hydrophilids have an elongated spine stretching across their body segements, while Dytiscids lack this. Here is an image of what their ventral sides look like:  
 Hydrophilid spine

Dytiscid ventral side

These are the main physical differences between the two, but there are other differences in their diet. Hydrophilids are scavengers, while Dytiscids are predators. However, Hydrophilids will occasionally prey on mosquito larvae. Dytiscids also dive to capture prey, hence the name predacious diving beetle. When ready to dive, the Dytiscid stores air under its wings to breathe while it is underwater. In order to be so agile in the water, Dytiscids are very well streamlined, in fact, so streamlined that males need to have suctions on their legs to grip females while mating! 

Even Baby Mosquitoes are Cute!

You are probably very much acquainted with the adult forms of these insects --- mosquitoes! The larvae dwell in standing freshwater, and those 'whiskers' on its head are bristles used for feeding and feeling for food, which contains algae and bacteria. Mosquito larvae breathe through spiracles, so they sometimes need to come to the surface of the water. They remain in water for seven to fourteen days before pupating. As larvae, all they do is eat and eat, thus growing bigger. Since all arthropods possess hard exoskeletons, the larvae must molt into a new exoskeleton to fit their current size. They go through four instars, or stages in between molts.  After the final molt, unlike dragonfly larvae, they form a pupa, and emerge not from their larval bodies, but from the pupa. 

What is this small monster? At your first glance, you may think it is some exotic insect, but in fact, it's not. It's just a dragonfly nymph! It is not common to see these, but if you have ever tried aquatic catching, you have probably pulled one up from the mud. Just like the adult form of these insects, the nymphs are highly predacious, feeding on other small aquatic invertebrates, especially mosquito larvae, and sometimes even small fish or tadpoles. Thus, the nymphs are important in biological pest control. The insects in this order(Odonata) experience incomplete metamorphosis, or hemimetabolous development. Once the dragonfly nymph has completed its final molt, it exits its aquatic world, and out of its 'backpack' emerges a fully grown dragonfly. Since insects have an open circulatory system, it takes a few minutes for the adult's wings to fill with hemolymph, the insect's blood. 

This is the larva of perhaps the most common insect that goes through complete metamorphosis, or holometabolous development --- the butterfly! This passage focuses particularly on swallowtail caterpillars. You can recognize them easily by their osmaterium, the Y-shaped protrusion that they emit when afraid. Not only does the osmaterium startle predators, it also produces a foul smell! In addition, most swallowtail caterpillars are vibrantly colored, or have eyespots. The butterflies may be beautiful, and the caterpillars, but despite this, some of these caterpillars are very destructive to plants. All caterpillars eat leaves, but some eat the leaves of crops or destroy trees. 

This is not a common larva to observe, but its behaviors are remarkable. They are underwater architects when it comes to pupating. Using silk from glands near their mouths, they stick together pebbles and bits of wood to form their pupae. Their pupae are also portable -- they can walk, while still being enclosed in the pupa. Their cases are open at both ends, enabling them to take in oxygen. If you want to see such a remarkable pupa yourself, you may want to try searching in a pond at your local nature preserve, because these larvae are very sensitive to polluted water, and can indicate water cleanliness. Here are some pictures of caddisfly pupae:

Normal pupa

Artistic pupae(out of gold and beads)! These larvae were in captivity.

Here are the larvae of a less enchanting insect: calliphorids, commonly known as blow flies. Just like the adults, the larvae, also known as maggots, eat rotting meat and carrion. However, maggots have been raised in captivity for a very surprising reason --- cleaning nonhealing wounds! Since the adults are potential disease vectors, and the fact that they feed on animal carcasses makes maggots a very unlikely possibility for medication. However, they are capable of eating the dead or infected flesh -- they just must be very clean! One problem with this therapy is the issue that maggots may also eat healthy tissue. 

Have you ever raised a captive insectivore? If so, you probably fed them this: a mealworm(as shown in picture above). These are the larvae of Tenebrionids, or darkling beetles. As well as being food for captive insectivores, mealworms are also considered pests, eating stored products.

What on Earth is this? It's an antlion larva! As the name suggests, they are ferocious predators of ants(notice the mandibles)! However, the way they catch them is truly unique. They dig a pit in a spiral pattern so that the walls slope downwards. Once that is done, they bury themselves in the sand, leaving only their jaws hanging open. A curious ant wanders close and begins to slip down the walls of the small pit. Trapped, the ant wanders around until it blunders into the antlion  larva's powerful jaws. 

                                                              A close-up of the mandibles