Platypus feed only in the water. The animals mainly find their invertebrate prey by searching along shallow riffles, gleaning items from submerged logs and branches, digging under banks or diving repeatedly to the bottom of pools.

Platypus foraging behaviour in a pool begins with an animal doing a neat, quiet duck dive. The animal swims to the bottom of the channel and uses its bill to detect and seize prey. Rather than waste time chewing its food underwater, the platypus temporarily stores prey items in cheek pouches located at the back of the jaw. It returns to the surface when its oxygen supply runs low (usually within 30-60 seconds of the time it dived, though dives of up to 138 seconds have been recorded) and then typically spends about 10-20 seconds masticating and swallowing food before again diving.

The use of dataloggers has confirmed that platypus mainly but by no means exclusively feed at night, with around 25% of animals tracked along a small Victorian stream and 40% of animals tracked in a Tasmanian lake observed to forage frequently during daylight hours.

Platypus typically have a varied diet dominated by insects (especially caddis fly larvae, but also larval and adult water beetles, water bugs, and larval mayflies, damselflies, dragonflies, dobsonflies, midges, craneflies and blackflies). They also dine on freshwater shrimps, snails, pea shell mussels, seed-shrimps (or ostracods), water mites and worms. Burrowing crayfish have been found to be an important part of the platypus diet at Lake Lea in Tasmania, and trout eggs are known to be consumed by animals occupying the Thredbo River in New South Wales.

After comparing the invertebrates found in different aquatic habitats with those identified in platypus cheek pouches, a researcher working in the Kangaroo Valley of New South Wales has concluded that platypus are particularly partial to the types of prey occupying edge habitats (defined as including pool margins and backwaters, the space below overhanging banks and among submerged vegetation and organic detritus), followed by those in pools and lastly by those associated with riffles.

The platypus’s ability to prey on sizable fish or other vertebrates is restricted by its lack of true teeth. Remains of a small frog (which may have been consumed as carrion) have been found in one platypus cheek pouch sample from the Shoalhaven River in New South Wales. A young platypus is equipped with true molars located at the back of the jaw, which fall out about the time that a juvenile first enters the water and begins to eat solid prey. The teeth are replaced by rough grinding pads which grow continuously to offset natural wear.

Because the platypus is a relatively small, warm-blooded animal, it needs substantial amounts of food to serve as fuel. Studies in captivity have shown that adult males require around 15-28% of their body mass in food each day to maintain good physical condition, with more food consumed in winter and spring than at other times of year. Similarly, the average daily food intake of animals occupying a Tasmanian lake has been estimated to be 19% of body mass. Not surprisingly, the amount of food eaten by lactating females increases markedly as their offspring grow. For example, daily food consumption by a mother of twins in captivity rose to around 80% of her body mass just before the young first emerged from the nesting burrow – roughly three times her daily food consumption in the months before she mated.

Further reading:
Bethge, P., Munks, S.A., Nicol, S. and Otley, H. (2000). The use of dataloggers to determine behavioural activity in the platypus. Australian Mammalogy 21: 262-263.

Bethge, P., Munks, S., Otley, H. and Nicol, S. (2003). Diving behaviour, dive cycles and aerobic dive limit in the platypus Ornithorhynchus anatinus. Comparative Biochemistry and Physiology A 136: 799-809.

Faragher, R.A., Grant, T.R. and Carrick, F.N. (1979). Food of the platypus (Ornithorhynchus anatinus) with notes on the food of brown trout (Salmo trutta) in the Shoalhaven River, N.S.W. Australian Journal of Ecology 4: 171-179.

Holland, N. and Jackson, S.M. (2002). Reproductive behaviour and food consumption associated with the captive breeding of platypus (Ornithorhynchus anatinus). Journal of Zoology (London) 256: 279-288.

McLachlan-Troup, T.A., Dickman, C.R. and Grant, T.R. (2009). Diet and dietary selectivity of the platypus in relation to season, sex and macroinvertebrate assemblages. Journal of Zoology 2009: 1-10.

Munks, S.A., Otley, H.M., Bethge, P. and Jackson, J. (2000). Reproduction, diet and daily energy expenditure of the platypus in a sub-alpine Tasmanian lake. Australian Mammalogy 21: 260-261.