A male sheep crab (Loxorhynchus grandis) is infected and feminized by a parasitic barnacle (Heterosaccus californicus). The parasite makes it stop developing fighting claws, and its abdomen widens to provide a “womb” that the barnacle fills with its brood pouch. Nurtured by the crab, thousands of baby barnacles hatch and disperse to infect anew.

After the flatworm (Ribeiroia ondatrae ) reproduces asexually inside a snail, its larvae find the tadpole of the American bullfrog (Lithobates catesbeianus) and burrow through its skin, forming cysts around the frog’s developing limbs. With legs added, subtracted, or compromised, it's easy prey for frog-eating birds like herons. Once inside the heron, the parasite is able to reproduce sexually. When the bird defecates, the parasite's eggs reenter the water, starting the cycle again by infecting new snails.

The female white butterfly wasp (Cotesia glomerata) is a parasitoid wasp that injects several dozen eggs into the caterpillar of the cabbage butterfly (Pieris brassicae). The eggs hatch and their larvae feed on the caterpillar's tissue until they are ready to emerge. They paralyze the caterpillar, chew their way out, and spin small yellow cocoons. Still alive, the caterpillar comes out of its paralysis, spins an additional layer around the parasitic wasp's cocoons, then stands guard over them, even protecting them by flinging its head back and forth when disturbed.

When spores of the mindsucking Ophiocordyceps fungus land on an Amazonian ant ( Dinoponera longipes), they penetrate its exoskeleton, enter its brain, and compel it to leave its normal habitat on the forest floor to scale a nearby tree. The dying ant, bursting with fungus, fastens itself to a leaf or another surface. Fungal stalks burst from the now-dead ant’s husk and rain spores onto the forest floor below, and onto more ants—beginning the process again.

The arboreal ant (Cephalotes atratus) feeds bird droppings to its own larvae. The droppings sometimes contain a parasitic nematode (Myrmeconema neotropicum) that, once inside, turns the ant's abdomen red and makes it look like a ripe berry. This attracts birds that eat the berry, which they do, thereby spreading the parasite far and wide in its droppings. The nematode also induces the ant to walk with its abdomen raised, in order to be extra enticing to birds.

When a wasp (Dinocampus coccinnellae) stings a ladybug (Coleomegilla maculata), it leaves behind a single egg. After the egg hatches, the developing larva eats the ladybug from the inside out, avoiding vital organs so as not to kill the host that keeps it alive. When the larva is ready to emerge, it exits the ladybug and spins a cocoon between its legs. Though the ladybug's body is now free of the parasite, it remains enslaved, standing over the cocoon and protecting it from potential predators.

The parasitic Hymenoepimecis argyraphaga wasp stings and paralyzes a Leucauge argyra spider, then deposits an egg on its abdomen. After the egg hatches, the larva holds onto the spider and feeds on its bodily fluids for a week. As the larva pupates, it forces the spider to rip down its own web and instead construct a custom-built web, consisting of only a few crossing strands, that will perfectly protect the larva's cocoon from predators. After the web is built, the larva drains the spider like a vampire, until it's dead, and proceeds with forming its cocoon.

Larvae of Paragordius varius, a parasitic worm, infiltrate a house cricket (Acheta domesticus) while it scavenges dead insects, then grow inside it. The cricket is terrestrial, but because the adult stage of the worm’s life cycle is aquatic, it alters the brain of the cricket so that it'll jump into the nearest body of water when it's fully grown and ready to emerge. The cricket may drown in the process, but a good amount of them actually survive.

The tiny amphipod (Hyalella azteca) lives its life out in the darkness of murky lake and pond bottoms—unless it's invaded by the larva of a thorny-headed worm (Pseudocorynosoma constrictum). The larva matures inside it, then forces it to abandon all reason and swim towards the light at the surface of the water. Unfortunately, ducks and other waterfowl, predators of the amphipod, are waiting for this exact thing to happen. It's all part of the larva's diabolical plan, as it can only grow to maturity in the guts of waterfowl. The parasite, turned orange by pigments from the amphipod's tissue, is happily eaten, along with the amphipod, by waterfowl who remains none the wiser.

A valley oak (Quercus lobata) sprouts pink spiny structures called galls after the spined turban gall wasp (Antron douglasii) lays an egg on one of its leaves. The egg hatches and when the larval wasp begins to chew on the oak leaf, it releases a chemical signal that instructs the tree to build galls around the developing wasp. The galls both protect the wasps and provide nutrients for them.