Hawk­moths by day and night

Two species of hawk­moth briefly cross paths in their search for nec­tar, as sum­mer days fade to night

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On a fine, still sum­mer evening, in a gar­den in the south-west of Eng­land, a pur­ple this­tle is in full bloom. The nu­mer­ous flo­rets that make up the flow­er­heads are rich in nec­tar, at­tract­ing a plethora of in­sects to feed. As dusk falls, a hum­ming­bird hawk­moth can be seen hov­er­ing over each flow­er­head. It sucks up the nec­tar with its long tongue, be­fore mov­ing rapidly onto the next flower, its wings a blur. Fi­nally, it has enough stored en­ergy to see it through the night. As the light be­gins to fade, it heads off to find a safe place to roost, among dense fo­liage. As it flies off, an equally fas­ci­nat­ing rel­a­tive emerges, for dusk marks the start of the day for this moth, not the end. The ele­phant hawk­moth is, like most moths, noc­tur­nal in its habits, tak­ing to the wing as night be­gins. Thus, the lives of these two in­sects briefly in­ter­sect. If this did not hap­pen, they would never meet, for one has evolved to be di­ur­nal, while the other is mostly noc­tur­nal. An­other ma­jor dif­fer­ence is that the ele­phant hawk­moth is res­i­dent in Bri­tain, whereas the hum­ming­bird hawk­moth is a sea­sonal mi­grant. It ar­rives here each spring and sum­mer in ever-in­creas­ing numbers as sum­mers get warmer. The hum­ming­bird hawk­moth is far scarcer and less wide­spread than the ele­phant hawk­moth. Its day­time life­style, how­ever, means it is seen more fre­quently.

Evo­lu­tion­ary traits

The hum­ming­bird hawk­moth’s name de­rives from its ap­par­ent sim­i­lar­i­ties to a hum­ming­bird. In a process known as con­ver­gent evo­lu­tion, the two un­re­lated species have de­vel­oped sim­i­lar traits to meet sim­i­lar en­vi­ron­ments. This mem­ber of the hawk­moth fam­ily has evolved a body shape, wing move­ments and flight ac­tion that are al­most iden­ti­cal to its avian coun­ter­part, even down to the hum­ming noise made by the wings. It has evolved to fill a niche as an aerial nec­tar feeder. It is a buff­ish-or­ange crea­ture, with grey forewings, or­ange hind­wings, a black-and-white che­quered body and a band across the tail. These are even sim­i­lar colours and pat­terns to those of some hum­ming­birds. The wings beat very rapidly, up to 70-80 times a se­cond, giv­ing the im­pres­sion of a blur to any­one watch­ing. The in­sect even has what ap­pears to be a face and beak. The for­mer is a se­ries of mark­ings on the head, the lat­ter, the thin pro­boscis which it uses to ob­tain nec­tar. Both bird and moth feed in the same way, by hov­er­ing in front of a flower while beat­ing their wings to stay in po­si­tion. Hum­ming­bird hawk­moths have a wing­span of 2-2¼in (5-6cm), not far short of the size of the small­est species of hum­ming­bird. But there is a big dif­fer­ence. Hum­ming­birds have only one pair of wings, whereas hawk­moths have two, their forewings and hind­wings. These work in ro­ta­tion to keep the in­sect aloft, and al­low them to ma­noeu­vre even bet­ter than the ac­tual hum­ming­bird.

They feed on a wide range of com­mon wild and gar­den plants. These in­clude hon­ey­suckle, lady’s bed­straw, red va­le­rian and phlox. They pre­fer those with plenty of nec­tar and a long ca­lyx, the col­lec­tion of sepals, which their pro­boscis en­ables them to reach more eas­ily than other in­sects. They are crea­tures of habit, of­ten flying around in a reg­u­lar cir­cuit, vis­it­ing the same plants again and again.

Early ar­rival

The first hum­ming­bird hawk­moths of the year are usu­ally seen in south-western or south­ern coun­ties of Eng­land in early May. They can ar­rive as early as April in fine springs, fol­low­ing southerly winds. These strong-flying in­sects have come all the way from Spain, Portugal, or North Africa. Some con­tinue much fur­ther. In Bri­tain, they have been recorded as far north as Orkney and Shet­land. They pre­fer warm, sunny day­time weather, but will also fly at dawn and dusk, and even dur­ing light rain. They have ex­cel­lent colour vi­sion, which is also very sharp, to en­able them to fix on a par­tic­u­lar flower while hov­er­ing to feed. Hum­ming­bird hawk­moths are long lived com­pared to other moths, with an adult life­span of two to three months. Af­ter mat­ing, the fe­males lay up to 200 spher­i­cal eggs, which mea­sure just 1mm across, from May on­wards. Each is laid on a sep­a­rate plant. They are pale green in colour, mim­ick­ing the buds of their main host plant, lady’s bed­straw. This helps them avoid the at­ten­tion of preda­tors such as birds. Other host plants in­clude hedge bed­straw, wild mad­der, and red va­le­rian. The eggs hatch be­tween six and eight days af­ter lay­ing. The lar­vae be­gin to feed avidly, so they can grow as quickly as pos­si­ble. When they hatch out, the tiny lar­vae are yel­low, but they soon turn green, with pale and dark hor­i­zon­tal stripes along the body and a blue ‘horn’ with a yel­low tip. They use these bright colours and oddly shaped head parts to scare off po­ten­tial preda­tors, such as song­birds. Ap­prox­i­mately three weeks af­ter hatch­ing, now ap­prox­i­mately 2½in (6cm) long, they pu­pate. The pupa drops to the ground, where its pale brown colour en­ables it to be dis­guised among the leaf lit­ter. Months later, in mid or late au­tumn, the pupa hatches into the adult hum­ming­bird hawk­moth. This new gen­er­a­tion then seeks out a shel­tered spot to hi­ber­nate for the win­ter. It may be in a hole in a wall or tree, or some­times in an out­build­ing, such

“Lovely in dye and fan, A-trem­ble in shim­mer­ing grace, A moth from her win­ter swoon Uplifts her face:” Wal­ter de la Mare, ‘The Moth’

as a shed or garage. How­ever, in Bri­tain, the win­ter cli­mate is usu­ally too cold for them to sur­vive.

Night-time flier

The ele­phant hawk­moth leads a very dif­fer­ent life­style to its cousin, be­ing both noc­tur­nal and res­i­dent. It is found through­out low­land Bri­tain and Ire­land, es­pe­cially in large ru­ral gar­dens, parks and wood­land edges. Bright golden-olive in hue, with vivid pink streaks across the body and wings, they are one of the most strik­ing of all Bri­tain’s in­sects. These colours and pat­terns ap­pear ob­vi­ous when the in­sect is seen in iso­la­tion, but they pro­vide sur­pris­ingly good cam­ou­flage when it is hid­ing among fo­liage. Here, the pink streaks help break up its out­line. Ele­phant hawk­moths have tri­an­gu­lar-shaped wings, with a wing­span of 1¾-2¾in (4½-7cm), and a broad body, ta­per­ing to the tip of the ab­domen. The name comes not from the ap­pear­ance of the adult, but from the larva. These are grey­ish-brown, and sport a pro­boscis that looks su­per­fi­cially like an ele­phant’s trunk. Two large false ‘eyes’ on the sides of its head ac­cen­tu­ate this, and give it a snake-like ap­pear­ance. When threat­ened by a preda­tor, such as a bird, the 3in (7.5cm) long cater­pil­lar swells up and waves its head in the air. This usu­ally has the de­sired ef­fect of fright­en­ing off the at­tacker. In Bri­tain, adult ele­phant hawk­moths are usu­ally seen from May to July. They emerge from their hid­ing places among plant fo­liage at dusk to feed on nec­tar-rich plants. They have very good night vi­sion, with light-sen­si­tive cells in their eyes. These en­able them to dis­crim­i­nate be­tween dif­fer­ent coloured flow­ers, when it would oth­er­wise be too dark for them to do so. Their pref­er­ence is for tubu­lar, nec­tar-rich flow­ers, such as those of hon­ey­suckle and wil­lowherbs. Eggs are laid on a va­ri­ety of plants, in­clud­ing fuch­sias, lady’s bed­straw and es­pe­cially rose­bay wil­lowherb. The cater­pil­lars emerge from July on­wards, and can be seen un­til Septem­ber. When the weather be­gins to turn cooler in the au­tumn, the cater­pil­lars pu­pate. They spend the win­ter in this form, hid­ing in shal­low soil, or in low veg­e­ta­tion, be­fore emerg­ing as adults the fol­low­ing spring.

Hov­er­ing above a this­tle, a hum­ming­bird hawk­moth sucks up nec­tar and mois­ture through its long pro­boscis, which is made up of two con­cave tubes hooked to­gether. When not in use, the pro­boscis, which is nearly as long as the moth’s body, is coiled up like a gar­den hose.

A hum­ming­bird hawk­moth cater­pil­lar, with its yel­lowtipped blue horn. The cater­pil­lars tend to be green when first hatched, turn­ing darker as they grow and moult the skin which no longer fits. The che­quered body and grey forewings of the hum­ming­bird hawk­moth. Its or­ange hind­wings are only evident in flight.

When star­tled, the ele­phant hawk­moth cater­pil­lar draws its trunk into its fore­most body seg­ment. This pos­ture re­sem­bles a snake with a large head and four large eye-like patches. › The green­ish-gold body of the ele­phant hawk­moth is punc­tu­ated by shocking pink stripes, which act as cam­ou­flage on many sur­faces.

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