Heavyweight Hexapods: The largest insects

The maximum size of insects is tightly constrained by their fundamental biology and atmospheric conditions.  Regardless, some insects push these constraints to their absolute limit.  Here I will talk about some of the largest living and extinct hexapods.

Lets begin with a summary chart.

Continue reading to hear about each of these insects…

The largest insect ever:
Meganeuropsis sp. (Protodonata)
2.5+ foot (72 cm) wingspan.

Meganeuropsis fossils. The left photo is superimposed with modern dragonflies with 4 inch wingspans. Photos by Ghedoghedo and Mark Sloan of Harvard Museum of Natural History.

Meganeuropsis lived during the Permian period, 248 to 290 mya. It belongs to the extinct order of griffinflies (Protodonata), related to dragonflies. Meganeuropsis grew to a wingspan of at least 2.5 feet. It is hypothesized that this animal could have weighed upwards of a pound. The largest modern relative of Meganeuropsis is the dragonfly Megaloprepus caerulatus, which can attain a comparatively meager wingspan of 7.5 inches, or 19 cm. There is some debate regarding how this flying insect was able to overcome physiological limitations to attain such great size. Discussion of this topic demands its own post in the future.

The longest modern insect:
Chan’s Mega-stick Insect, Phobaeticus chani (Phasmida)
14.1 inches (35.8 cm) head to tail, 22.3 inches (56.7cm) including legs.

Photos: London NHM.

This stick insect was recently discovered in a private collection from the rain forests of Borneo, in 2008. It beat the previous record holder for longest insect, Phobaeticus serratipes, by about half an inch. Little is know about the ecology of P. chani as there are only three existing specimens, but it probably lives high in the jungle canopy. One bizarre feature of this animal is that its eggs have wing-like protrusions, possibly used for wind dispersal after being laid. Read more about P. chani, and watch a video, at the London Natural History Museum Website.

The heaviest modern insects
This category is surprisingly contentious, with several species competing for the title of Largest Insect. Let’s take a look at all of the claimants.

-Little Barrier Island Giant Weta, Deinacrida heteracantha (Orthoptera)
2.5 ounces (71 grams), gravid female.

Giant Wetas, related to crickets, are found primarily on islands surrounding New Zealand. The large size of these animals is a great example of island giganticism. The heaviest recorded weta is the Little Barrier Island Giant Weta, Deinacrida heteracantha, at 71 grams. However, this weight comes with a caveat in that it was measured form a captive, unmated, extremely gravid female, carrying a full brood of developed eggs. Without eggs, these giant wetas only reach about 35 grams.

The true, but mostly unconfirmed, contenders for heaviest insect are all beetles (Coleopterans):

Size comparison of the worlds largest known beetles. The ghosted 9+ inch titan beetle on the left is only reported anecdotally. Figure adapted from Williams, 2001.

-Goliath Beetle, Goliathus goliatus (Coleoptera)
Adult: 4.3 inches (11 cm), 1.5+ ounces (42+ grams)
Larva: 5 inches (13 cm), 4.1 ounces (115 grams)

Adult and larval forms of G. goliatus. Photos by Matthias Frei and Karl Meier.

The adult male Goliath Beetle gets big, but its own larval grub form boasts the greatest bulk. Learn more about these African Scarabs here. If you wish to have your own cuddly Goliath grub, there is also a breeding guide.

-Titan Beetle, Titanus giganteus (Coleoptera)
Adult: 6.5 inches (16.7 cm), possibly up to 9 inches.
Larva: Has never been found

Despite the size of gravid Giant Wetas and Goliath Grubs, there is another poorly understood contender from the Amazon. The Titan Beetle grows to at least 6.5 inches in length (one report from from 1874 puts it at 9 inches, but may have included the animal’s antenna). After pupating, the adult Titan Beetle starts to die. It doesn’t eat, and instead searches relentlessly for a mate. The larval form of the Titan Beetle has never been found. It is hypothesized to live in wood and take years to mature to adulthood. Bore holes, possibly made by the Titan Beetle grub, have been found to be two inches in diameter, and could have housed a grub a foot in length.

If you have Real Player, you can watch the segment on the Titan Beetle from “Life in the Undergrowth” here.

References:
Moffett, M. W. 1991. Wetas – New Zealand’s insect giants. National Geographic, 180(5): 100-105.

Walker, T. J. 2001. University of Florida Book of Insect Records, 2001. http://entomology.ifas.ufl.edu/walker/ufbir/.