Animals that pre-digest their food may sound like something out of a science fiction film, but of course they’re very real – and what they’ve done is evolved a splendid solution to the ecological issues they face.
What’s interesting – as illustrated in the examples below – is the variation in the systems they’ve come up with. Which one do you think is best?
8 animals that liquidise their prey before slurping them up like a smoothie
Spiders
Spiders are one of the best-known examples of animals that digest their prey outside of their own bodies. This ability almost certainly simultaneously evolved with both the use of silk webs to trap animals often larger than themselves and the use of venom to subdue them.
Because – if they didn’t first liquidise the internal nutritional contents of the insect or some other invertebrate they have trapped – how would they eat it?
Scientists who have studied the process say spiders “pump and suck digestive fluids and liquified tissues back and forth between the prey and the gut”, so that the prey animal itself becomes the digestion chamber. Yummy.
Scorpions
Though also arachnids like spiders, scorpions – for which there are fossil records going back more than 400 million years – have a slightly different method of pre-digesting their meal.
- What’s the most venomous scorpion in the world? And just how deadly is it?
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Like spiders, they possess often powerful venoms with which to kill animals ranging from insects and other arachnids to even snakes, lizards and rodents, but they then use the sharp, pincer-like mouthparts called chelicerae to tear off small pieces of flesh.
Between these chelicerae is the so-called ‘preoral cavity’, which is then supplied with juices from the gut to partially digest the food before it is taken into the body. Scientists say scorpions are highly efficient eating machines and “can increase their body weight by one third” in one meal. They can live without food for up to 12 months and may only feed 5 times a year.
Assassin bugs
Often brightly coloured and with no obvious deadly hardware such as a scorpion’s stinger, assassin bugs could be mistaken for any common or garden insects of no great threat. But looks can be deceptive, and the long proboscis they possess is the giveaway.
This enables them to deliver a fatal dose of a venom containing peptide neurotoxins to their unsuspecting prey – a toxin that also starts the liquification process inside the body of the animal. This same hypodermic needle can then suck up the gooey mush. This way they can feed on a wide variety of insects, including flies, beetles, caterpillars and aphids – some are even used in agriculture to control crop pests.
Green lacewings
Adult green lacewings are non-predatory, feeding on pollen, nectar and honeydew, but their larvae, known as aphid lions are voracious predators. Like assassin bugs, they look relatively unthreatening with slender, humpbacked bodies and no distinctive armoury with which to attack their prey.
But, scientists have found, they utilise pincer-like mouth parts to inject a venom that both paralyses and liquifies their hapless victims. They live on plants, trundling around in search of mites, aphids and other small insects to fuel their lifestyles. They are regarded as effective controllers of pest aphids.
Octopuses
It almost seems unfair. Not only does the Mexican red octopus possess eight arms with which to seize and restrain its prey and a sophisticated brain with which to plan its attacks but also – it turns out – a saliva that paralyses and predigests prey such as blue crabs of which it is fond.
Crabs are a relatively easy meal, but they they possess both a hard carapace and of course sharp pincers that could injure the octopus. They hold the crustaceans firmly with their arm suckers and bring them up to their mouths, at which point they inject the paralysing and liquifying saliva via special glands, though exactly how they do this is unclear and varies.
The curled octopus, for example, delivers its deadly package through punctures in the eyes. Some octopuses are even cannibalistic, so presumably they even know what’s coming if they’re attacked by their own kind.
Centipedes
The Tanzanian blue ringleg, also known as the red-headed centipede, is part of the Scolopendra genus which includes some of the largest and most venomous terrestrial invertebrates on Earth.
This particular species grows to around 13cm, though some can reach a foot long. But that’s not the scariest thing about them – like all centipedes, the blue ringleg has a pair of so-called forcipules, which are actually modified front legs, through which it delivers a venom that is similar in its composition to that of black widow spiders.
And, finally, if that wasn’t quite enough to make them one of the most terrifying animals on the planet, this injectable toxin also contains other compounds that act to digest the food, making consumption that bit easier. Despite its name, it is naturally found in Australia as well as large parts of Africa and southern Asia, and has been introduced to North and South America. It’s been suggested that international shipping is responsible for its spread.
Starfish
Any animal that liquidises its prey is enough to inspire thoughts of creatures from other planets, but surely the bizarre feeding ecology of the starfish makes it appear even more alien.
That’s because it approaches its victims – mussels or clams are two favourites – and then distends its stomach out of its body and over the intended food item where it partially digests it into what has been described as a soup-like chowder.
Both stomach and chowder are then taken back into the body, where the digestion process is completed. Bet you’re glad you’re not a shellfish now.
Velvet worms
They might sound sweet, and if not exact cuddly then relatively benign, but velvet worms are anything but. A study of one species, Macroperipatus torquatus (it doesn’t have a common name), which is found in Trinidad’s tropical rainforests, found that it probes for food in the leaf litter with its antennae.
They prod potential victims to assess them for both size and nutritional value, and once it has found something suitable, it squirts out a sticky, proteinaceous goo from papillae (small, rounded protuberances) either side of its jaws, which entangles the target. Immobilising and partially digesting saliva is then injected into the victim, before the flesh is consumed – the last stage of the process is slow and can take several hours.
