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Yellowjackets may be confused with other wasps, such as hornets and paper wasps such as Polistes dominula. A typical yellowjacket worker is about 12 mm (0.47 in) long, with alternating bands on the abdomen; the queen is larger, about 19 mm (0.75 in) long (the different patterns on their abdomens help separate various species).
Yellowjackets are sometimes mistakenly called "bees" (as in "meat bees"), given that they are similar in size and general coloration to honey bees, but yellowjackets are actually wasps. In contrast to honey bees, yellowjackets have yellow or white markings, are not covered with tan-brown dense hair on their bodies, and do not have the flattened, hairy pollen-carrying hind legs characteristic of honey bees (although they are capable of pollination).
Yellowjackets have lance-like stingers with small barbs, and typically sting repeatedly, though occasionally a stinger becomes lodged and pulls free of the wasp's body; the venom, like most bee and wasp venoms, is primarily dangerous to only those humans who are allergic or are stung many times. All species have yellow or white on their faces. Their mouthparts are well-developed with strong mandibles for capturing and chewing insects, with probosces for sucking nectar, fruit, and other juices. Yellowjackets build nests in trees, shrubs, or in protected places such as inside man-made structures, or in soil cavities, tree stumps, mouse burrows, etc. They build them from wood fiber they chew into a paper-like pulp. Many other insects exhibit protective mimicry of aggressive, stinging yellowjackets; in addition to numerous bees and wasps (Müllerian mimicry), the list includes some flies, moths, and beetles (Batesian mimicry).
Yellowjackets' closest relatives, the hornets, closely resemble them but have larger heads, seen especially in the large distance from the eyes to the back of the head.
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The predecessors of silverfish, along with those of jumping bristletails, are considered the earliest and most primitive insects. They evolved at the latest in mid-Devonian and possibly as early as late Silurian more than 400 million years ago. Some fossilized arthropod trackways from the Paleozoic Era, known as Stiaria intermedia and often attributed to jumping bristletails, may have been produced by silverfish.
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Silverfish are able to digest cellulose by themselves, thanks to the cellulase that is produced by their midgut. They consume matter that contains polysaccharides, such as starches and dextrin in adhesives. These include book bindings, carpet, clothing, coffee, dandruff, glue, hair, some paints, paper, photos, plaster, and sugar. They will damage wallpaper in order to consume the paste. Silverfish can also cause damage to tapestries. Other substances they may eat include cotton, dead insects, linen, silk, leftover crumbs, or even their own exuviae (moulted exoskeleton). During famine, a silverfish may even consume leather and synthetic fabrics. Silverfish can live for a year or more without eating if water is available.
Silverfish are considered household pests, due to their consumption and destruction of property. However, although they are responsible for the contamination of food and other types of damage, they do not transmit disease. Earwigs, house centipedes, and spiders such as the spitting spider Scytodes thoracica are known to be predators of silverfish.
The essential oil of the Japanese cedar Cryptomeria japonica has been investigated as a repellent and insecticide against L. saccharinum, with promising results: filter paper impregnated with a concentration of 0.01 mg/cm3 of essential oil repelled 80% of silverfish, and an exposure to vapours of 0.16 mg/cm3 for 10 hours caused a 100% mortality rate.
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Some species make a buzzing noise while other cockroaches make a chirping noise. Gromphadorhina species and Archiblatta hoeveni produce sound through the modified spiracles on the fourth abdominal segment. In the former species, several different hisses are produced, including disturbance sounds, produced by adults and larger nymphs; and aggressive, courtship and copulatory sounds produced by adult males. Henschoutedenia epilamproides has a stridulatory organ between its thorax and abdomen, but the purpose of the sound produced is unclear.
Several Australian species practice acoustic and vibration behaviour as an aspect of courtship. They have been observed producing hisses and whistles from air forced through the spiracles. Furthermore, in the presence of a potential mate, some cockroaches tap the substrate in a rhythmic, repetitive manner. Acoustic signals may be of greater prevalence amongst perching species, particularly those that live on low vegetation in Australia's tropics.
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