Catocala fraxini is a moth of the family Erebidae. It is commonly known as the blue underwing. It was initially described by Carl Linnaeus in the 10th edition of Systema Naturae, published in 1758. The species is endemic to most of central Europe, northern Europe, and parts of southern Europe. It is found in much of the Palearctic, Turkey, Siberia, the Russian Far East, Korea, and Japan. It is absent from Portugal, the Mediterranean islands, Greece, northern Scotland, northern Scandinavia and southern Russia.

The forewing is white and yellow. The pattern is irrorated with pale or dark grey colouration, which sometimes features a yellow accent. The inner and outer lines are dark. These are serrated and bilateral. The median and subterminal lines are dark and serrated. The reniform stigma features a black centre and outline. There is a pale diamond-shaped yellow pattern outlined with black beneath this. The hindwing is dark, with a broad blue postmedian band.

The larvae are brownish grey and black accented. These have pointed sections on the 9th and 12th segments.

The caterpillars feed on various species of poplar, or other species within the Populus genus.

Two subspecies of this taxon exist. The Adscita statices statices is found in Spain, in most of central and eastern Europe, in Siberia, Turkey, and China. Adscita statices drenowskii is found in the Balkans and Turkey.

The topographical distribution of each subspecies ranges from dry, sandy, and calcareous habitats to montane locations, and wet meadows and marshes.

Both subspecies are visually similar to the Scarce Forester (Adscita globulariae) and Cistus Forester (Adscita geryon). Adscita statices are often found feeding at flower species, including those within the taxon Rumex. Devil's-bit scabious, field scabious and marsh thistle are further frequent.

The wingspan of the species is 25 to 28 millimetres in length. The antennae, head, thorax, legs and abdomen are vibrant green, although the thorax can be occasionally blue toned and iridescent. The wings may appear rusty-red in the early morning and evening due to its coloured scales, which feature pores that can fill with water and visually change in hue. The wider forewings are less glossy than the body. These are mostly blue green, but can also be green to yellow green. The edges of the wings are black-grey. The hindwings are moderately wide. These feature a slightly truncated rim and are slightly transparent, with a blackish grey hue that is lightened basally. Both forewings and hindwings have a grey underside.

The caterpillars are pale yellow-green. There is a central dark stripe vertically across the larvae, and white hairs on the dorsal sections.

The species may overwinter as larvae. These first mine the leaves, then feed on the lower leaves. The larvae pupates in a cocoon spun near the ground, which is concealed amid vegetation.

The species exists with a distribution between southern Europe, Asia, the Middle East, and North Africa. It can be found within the warmer regions of Europe, between France and Portugal to the Balkans, Italy, Ukraine, the Corsican and Sardinian islands, Austria, and Switzerland. The Asiatic and Middle ranges include Georgia, Azerbaijan, Turkey, Iraq, Iran, Syria, and Lebanon.

The primary habitats of Saturnia pyri are dry, hot, and open spaces with small trees and shrubs, including taxonomic genera such as Prunus, Pyrus and Crataegus. The Persian walnut, Juglans regia, is a preferred species as the caterpillars can use the toxic compounds from the walnut as a defence. Moth eggs are white-grey and laid on the underside of leaves when undisturbed, in rows of ten. The eggs hatch after 11 to 20 days with the influence of temperature. Caterpillars are typically black with brown tubercles. The tubercles turn orange in the second instar. During the third instar onward, caterpillars gain green colouration with yellow and blue tubercles.

Pre-pupae caterpillars are orange with vibrant spots. Cocoon spinning occurs between twigs, in bark or between the ground and the base of the tree. Rocks, dead wood and the crown of the trees are not unusual. The cocoons are brown and are up to 5 centimetres in length. The pupae may be able to overwinter for more than a year in some cases.

The species is the largest European moth. It has a wingspan reaching 15 to 20 centimetres in length.

The Grey Dagger can be found in Europe, North Africa, northern Iran, central Asia, southern and central Siberia, Mongolia, and the Levant. The species mainly inhabits deciduous forests, hedgerows, parks and gardens. The range occurs at an elevation up to 1,600 metres above sea level.

The wingspan is between 34 to 45 millimetres in length. Grey forewings with bold black dagger-shaped markings are typical. The hindwings are ashy grey and often paler in the male due to dimorphism. The species is very similar to the dark dagger (Acronicta tridens). Identification occurs through slight differences in colouration. The grey dagger is darker in colour than the dark dagger and always lacks the white hindwings often present in the male of the dark dagger species. The larvae of the two species further are very different.

The larva of Acronicta psi has many bristle-like saetae. The larvae are grey or brown in colouration underneath and black on the upper side. Red spots exist along the lateral sides and a yellow stripe exists along the back. It has a distinctive horn behind the head area, which is absent from the larva of dark dagger moths.

The grey dagger flies during the night from June to August. It is attracted to light and sometimes sugar. It feeds on a wide range of plants: mainly trees and shrubs. Noted food plants include ground-elder, alder, birch, hazel, hawthorn, apple, red robin, poplar, plum, pear, oak, rose, bramble, willow, lime, and elm. The species overwinters as a pupa.

This is a common species in Europe and the Near-East.

The moth is large, with a wingspan between 50 to 62 millimetres. It is butterfly-like in morphology. The entire adult is coloured white to pale yellow, and marked with faint specks to the fascia.

The moth flies at night from June and July. It is attracted to light, which can occur in large numbers. The eggs are orange. These feature about 16 longitudinal keels, which have transverse lineations between the keels. The larva is grey-brown. Colouring on the larvae is arranged consecutively in faint longitudinal lines. The larva is twig-like and feeds on a variety of trees and shrubs. Elder, hawthorn, honeysuckle and ivy are notable. The species can overwinter as a larva.