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Parasites both captivate and disgust us, and we've already uncovered some of the truly bizarre parasites that exist. However, evolution is a relentless race of adaptation, with many defenses against parasites proving to be even more astonishing than the parasites themselves.
10. The Caterpillar's Rear-Firing Cannon
The leaf-rolling caterpillar is the juvenile stage of leaf-wing butterflies. It camouflages by spending its early days at the tips of leaves and later, in its adult form, mimics dead foliage. In between these stages, it becomes large and easy prey for predators, so it rolls itself into a leaf shape and adopts a still, hidden lifestyle.
However, this quiet life brings a major challenge. The caterpillar needs to defecate, but its feces’ scent alerts both predators and parasites to its location. To solve this, the leaf-roller has developed a unique method, known as 'fecal firing.'
A network of blood vessels beneath its anal plate expands, building pressure. Once enough waste has built up, the ring releases, launching the caterpillar’s feces with force that can be up to 300 times the caterpillar’s weight. This action occurs roughly every 20 minutes.
With its waste safely ejected, the leaf-rolling caterpillar relaxes securely in its leafy shelter, free from parasites and ready to transform into a butterfly.
9. Parasitic Infections Can Make Some Animals More Sexual
Parasites have a cruel tendency to weaken their hosts, making them less viable than their uninfected counterparts. They may stunt development, shorten lifespans, or even induce sterility to further their own reproductive agendas. Infected organisms leave behind fewer offspring, which is disastrous for any species.
Some species fight back against parasitism by increasing their sexual activity. In response to a shortened lifespan, and with sterility looming, these species mate much more frequently, attempting to pass on their genes before it's too late.
A prime example of this is the New Zealand freshwater snail. Studies have shown that snails exposed to parasitic worms not only increase their mating frequency but also engage with more mates. This behavior boosts their chances of passing on their genes and helps stabilize populations in their environment.
8. The Enemy of My Enemy
Plants are unable to escape from predators. They lack both an immune system and a nervous system. So, how do plants detect threats and defend themselves against parasites and predators? By evolving into living fortresses and factories of biological weapons.
Plants have incredibly robust cell walls that protect them from insects and microbes. Their structures also prevent other organisms from climbing or reaching vital areas. Many plants produce hydrogen peroxide to guard against fungal or viral attacks and contain a variety of toxins designed to kill predators or make themselves unappetizing.
Many plants have evolved defenses so intricate and specific that they left scientists puzzled for years. Despite lacking any system to sense pain, plants are able to distinguish between a natural tear or rupture and the bites of certain predatory or parasitic species. Even more remarkable, these plants release a chemical alarm made up of volatile organic compounds (VOCs), which attract a specific predator to deal with the parasite harming the plant.
For example, when spider mites attack apple trees or lima beans, the plants release VOCs that attract other mites which prey on the spider mite. Similarly, when moth larvae infest cotton plants, the plants release VOCs that summon wasps, which lay their eggs inside the larvae. In one experiment, when aphids overran cucumber plants, the plants emitted VOCs that specifically drew in ladybird beetles, which devoured the aphids and halted the outbreak.
The insects inadvertently contribute to their own downfall by converting plant matter into chemicals known as peptide elicitors. These elicitors are then secreted back into the plants during subsequent feedings. The plants detect each elicitor and respond by emitting VOCs to call for assistance.
7. Eastern Screech Owls Befriend Blind Snakes
The eastern screech owl has come up with a strange and eerie solution to the issue of ectoparasites. Typically, these owls provide their young with dead food—except in one case. The exception is Leptotyphlops humilis, a snake with rudimentary eyes that resembles a large earthworm. While the owls occasionally consume these snakes, they more often drop them into their nests, where both adult and young owls leave the squiggly reptiles untouched.
The snakes reside in the nest, feeding on insect larvae within the nest debris. This greatly lowers the likelihood of the young contracting parasites—nests that house live blind snakes allow the owlets to grow faster and enjoy a lower mortality rate.
Urban birds have developed a variation of the blind snake tactic. They line their nests with cigarette butts, which help eliminate parasites like ticks and mites. They prefer butts with higher nicotine content, as these are more effective in killing parasites.
6. Self-Medication
Dogs and cats frequently consume grass, which they are unable to digest. This behavior is likely a vestige from when they ate plants to help clear intestinal worms. Younger animals, who are more vulnerable to infection, tend to eat more grass than older ones.
Many primates, especially chimpanzees, consume whole leaves and plant piths to counteract parasites and the digestive issues they cause. Remarkably, they even separate the medicinal part of the plant piths from the surrounding toxic parts. Chimpanzee self-medication is so advanced that they use many of the same natural remedies for malaria and diarrhea that African traditional healers employ.
The insect world isn't left out either. Butterflies, ants, fruit flies, and moths have all been observed using plants for medicinal purposes. Some insects even act like doctors, tending to other sick members of their species.
5. Termites Wall Off Their Infected Comrades
Termites are as resilient as cockroaches, and they’re just as hard to eliminate. A particularly invasive species, the Formosan termite from China, is considered practically impossible to completely eradicate once its colony is established. This is true whether the would-be eradicator is human, nematodes (roundworms), or viral parasites that prey on them.
Termites also rank among the most fearsome creatures on the planet. Some of their soldier castes are downright terrifying, and the gut protozoa that live symbiotically within them are aptly named Cthulhu and Cthylla. They are so ruthlessly effective that older, less useful members of some species develop blue crystalline explosive proteins and are sent on suicide missions against rival colonies.
Humans have attempted to combat these terrifying creatures using parasites, replacing chemicals and pesticides with nematodes. However, termites have a harsh and often effective way of dealing with parasitic infections. When one termite becomes infected, the others quickly wall it off in a small chamber, where it is buried alive and starves to death, effectively eliminating both the infected termite and its parasites.
4. Bees Save One Another With Fecal Cocktails
Swiss researchers investigating bumblebees and the parasites that affect them have made a fascinating discovery. The bees exchange feces that contains bacteria capable of fighting off Crithidia bombi, a parasite that mainly targets the queen.
Hauke Koch and Paul Schmid-Hempel, along with their team, found that bees who received a ‘fecal cocktail’ from their nestmates were much less affected by Crithidia bombi compared to bees that were given artificially grown feces or sugar water. The bacteria were shared socially among the bees, not individually. While scientists aren’t sure exactly how the bacteria protect the bees, they hope that this research will provide insights into our own gut bacteria and its protective role.
Other bees make a huge sacrifice to protect the colony from parasites, detaching themselves from several parts of social bee life. While it was once believed that sick honey bees were driven out of the hive, it’s now understood that the process is altruistic—these bees willingly go away to die.
Even more remarkably, infected bees strive to remain as helpful as possible for as long as they can, while minimizing actions that might infect others. They stop feeding the queen, leave the hive during the night (when other bees are huddling for warmth, an ideal time for infection to spread), and take on more dangerous foraging tasks, such as venturing out in bad weather.
Bees aren’t the only insects exhibiting this behavior. Infected carpenter ants also decrease their social interactions, avoid engaging with the brood, and spend the majority of their time away from the nest.
3. Sexual Reproduction May Have Evolved As A Defense Against Parasites
Sexual reproduction is an energy-intensive strategy. It requires more resources, takes up more time, and results in less genetic information being passed on compared to asexual reproduction. However, offspring produced sexually are much more genetically diverse, which increases their chances of developing beneficial traits, such as resistance to parasites and pathogens. Species capable of both sexual and asexual reproduction prefer to reproduce asexually when parasites are not a threat. But when faced with a parasite-heavy environment, sexual reproduction flourishes.
An Indiana University study focused on a microscopic roundworm (Caenorhabditis elegans) and its parasitic bacterial invader (Serratia macrescens). The roundworms were divided into three breeding groups: asexual, sexual, and a hybrid of both. After exposure to the parasite, the asexual worms quickly became extinct, while sexual worms thrived, and the worms that could switch between reproductive modes remained asexual only in the absence of parasites.
So the next time you embrace your partner, take a moment to thank a parasite for the reason behind your reproductive success.
2. Ants and Phoridae Flies: A Deadly Dance
Leaf-cutter ants must not only defend their precious fungal gardens but also protect themselves from parasites. Living in large, social colonies, ants are prime targets for opportunistic parasites. Among the most dangerous are the Phoridae flies, which parasitize ants by laying their larvae inside them, transforming the ants into zombie-like creatures. A particularly gruesome species of Phorids even targets the ants' anus to lay its eggs.
The ants’ first line of defense is early detection. The presence of a single fly sends an entire colony into defensive mode, where the ants flail their appendages wildly to prevent the fly from reaching its target. Spines and tough hairs cover their bodies to help deter or injure the attackers.
The leaf-cutter ants have a second line of defense that is specific to their species. A caste called “minums” or “hitchhikers” ride along on bits of cut leaves, performing the task of cleaning parasitic fungi off the leaves. One of their key duties is to help ward off phorid flies. Since minums are too small to be infected themselves, they are perfectly suited for this role.
If a fly manages to bypass all of the defenses, the ants will fight back by biting the fly, rolling into tight balls, lowering their abdomens, or simply running erratically to avoid the fly. Some ants even pull their heads tightly against their thorax, making it impossible for the fly to lay its eggs or causing it to lose its egg-laying appendage.
The phorid fly waits along the trail, needing only a fraction of a second to deposit its eggs. The encounter is a deadly game, with both species engaged in a fight for survival. If the fly fails, it cannot pass on its genes. If the ant fails, it faces a grim fate.
1. Ants and Microbes Create Parasite Dump Sites
Attini ants process leaves into a paste that serves as nourishment for their fungal colonies. These ants cultivate their colonies like a garden, using them both as a food source and a shelter. To safeguard their gardens from soil parasites, the ants keep them elevated from the ground. However, when a fungus parasite called escovopsis arrives, the ants require a more refined defense.
In response, the ants forged an evolutionary partnership with Actinomycetous, a symbiotic bacterium that inhabits specialized pockets in the ants' mouths. As the ants care for their gardens, they deposit any escovopsis they encounter into these pockets. The actinomycetous bacteria then produce antibiotics, and the ants subsequently expel a hard pellet made entirely of parasitic material.
Instead of discarding the pellet far from the colony, the ants designate a specific area within the colony to store it. In some species, the ants go even further by stacking and carefully tending these pellets until they form a type of parasite landfill.
