Determining the largest insect ever is complex because the title depends on the metric used—mass, length, or wingspan—and whether the comparison includes species living today or the giants of the deep past. A single champion cannot be named, but rather a list of record-holders. Modern insects are constrained by physical laws, meaning the largest species alive now are dwarfed by their prehistoric relatives.
How Insect Size is Measured
Entomologists use three primary measurements to determine the “biggest” insect. Mass or weight is typically applied to bulky insects like beetles and orthopterans, where sheer volume dictates the record. Length is measured either by body length alone or by the total span including extended appendages, a method favoring elongated species like stick insects. Wingspan measures the distance from wingtip to wingtip when the wings are fully spread. This metric is used for flying insects, such as moths and butterflies, where the surface area of the wings is the most impressive feature. These three measurements allow for a comprehensive view of maximum insect size.
The Largest Living Insects
Living insect champions demonstrate the variation in size metrics across the class Insecta. For sheer bulk and weight, the Goliath Beetle (Goliathus goliatus) is a primary contender, with larvae reaching weights over 100 grams (3.5 ounces). A verified adult weight record of 71 grams (2.5 ounces) is held by a gravid female Giant Wētā (Deinacrida heteracantha). The record for the greatest length belongs to the Chinese stick insect, Phryganistria chinensis, which can reach a total length of 64 centimeters (25 inches) with its legs fully extended. For wingspan, the White Witch Moth (Thysania agrippina) holds the title, with verified specimens measuring over 30 centimeters (12 inches) across.
The Largest Extinct Insects
To find the maximum size insects have ever attained, one must look to the fossil record of the Paleozoic Era. The largest insect is the griffinfly Meganeuropsis permiana, a distant relative of modern dragonflies. This prehistoric giant, which lived during the Permian period, possessed a wingspan estimated to be up to 75 centimeters (30 inches). This gigantism was facilitated by a unique atmospheric condition during the Carboniferous and early Permian periods. Atmospheric oxygen levels were significantly higher than they are today, reaching up to 35 percent. This oxygen-rich environment allowed the Meganisoptera order to evolve to immense proportions, dominating the skies long before the appearance of birds.
Biological Limits to Insect Size
Modern insects are smaller than their prehistoric counterparts due to their unique respiratory system, which limits the distance oxygen can travel within the body. Insects do not use blood to transport oxygen; instead, they rely on a network of tubes called tracheae that deliver air directly to the tissues through passive diffusion. At the current atmospheric oxygen level of 21 percent, diffusion is too slow to supply oxygen to the core of a large body. The exoskeleton also limits size, as it must be shed and regrown during molting (ecdysis). As an insect increases in size, its mass increases faster than the surface area of the exoskeleton, following the square-cube law. A large insect would collapse under its own weight during the vulnerable molting period, when its new outer layer is soft. The metabolic cost and physical vulnerability of molting further prevent modern insects from reaching the giant sizes of the past.