Determination sheet 1 September 2026 Copenhagen, Denmark — indoors 44 photographs

A crane fly on a wall, keyed to Tipula paludosa

A single male crane fly, photographed on an interior wall over about six hours with a phone. This is the determination in full: what each character rules in or out, what the photographs can bound about its age, and where the evidence stops.

A key is a sequence of forced choices, so these steps are numbered: each only makes sense once the one above it is settled. Green dots mark characters visible in the photographs; red squares mark characters that rule something out.

Sex has to be established before the species characters mean anything, because several of the standard couplets in Tipula apply to one sex only. Here the abdomen tip answers it immediately.

The abdomen ends in a blunt, swollen, glossy chestnut capsule — a hypopygium, the male genital capsule. A female would taper to a hardened, upcurved ovipositor, which is conspicuously absent. This is the single most common sticking point when identifying crane flies from photographs: the abdomen tip is the most obvious thing about them and it is strongly sexually dimorphic, so a male compared against a photograph of a female reads as damaged rather than as the other sex.

With the specimen established as a large male Tipula, one countable character separates Tipula paludosa from the rest of the genus.

13 antennal segments is the norm across the genus Tipula; paludosa, with 14, is the exception (NatureSpot; genus account). It is worth being exact about what that means: the count is a test for paludosa against the whole genus, not a two-way choice between paludosa and any single other species. Treating it as the latter is an easy and consequential mistake.

The wing-length character sometimes quoted alongside it — wings shorter than the abdomen in paludosa, as long as the abdomen in T. oleracea — separates females and is no help for a male.

Eleven joints delimit twelve flagellomeres. The first is plainly the longest — about 1.5× its neighbour — which is the detail that makes the base interpretable at all: an unusually short dark piece at the base of an antenna is a pedicel caught in shadow, not a first flagellomere.

This count is unusually sensitive to which frame it is taken from, in a way worth stating plainly. A backlit antenna darkens the pale pedicel until it reads as part of the flagellum, adding a segment that is not there. An antenna angled away from the camera foreshortens the basal segments, compressing exactly the region where the boundary has to be judged. Both errors push the count the same way. The frame used here avoids both: the antenna lies across the plane of the wall, side-lit, sharp from base to tip.

The date corroborates rather than carries the determination. The first of September sits on the peak emergence of T. paludosa, which has one generation a year and produces the familiar wave of large crane flies entering houses across northern Europe at exactly this time (Cornell CALS). That is an argument from base rates; on its own it would not be enough, and it is precisely the reasoning behind a great many misidentifications — plain-winged beige crane flies are routinely filed under paludosa by default (iNaturalist taxon flag).

Held at probable rather than confirmed for one reason: the terminal flagellomeres shorten toward the tip, and an error of ±1 there cannot be excluded from a photograph. A specimen under a hand lens would remove it.

No character in a photograph gives an insect's age in days. What the frames do support is a bracket, read from wear — and for this species the bracket is narrow, because the adult stage is very short.

Tipula paludosa adults do not feed. They emerge on the reserves laid down by the larva, and live roughly 7–14 days; mating and most egg-laying happen within the first 24 hours (Cornell CALS; Northeastern IPM Center). Nearly the whole life of the animal is spent as a larva in soil; the adult is a brief dispersal-and-mating stage.

Not newly emerged. Two things put a floor under the estimate:

• The cuticle is fully hardened and pigmented. The thoracic pattern is defined and the abdominal banding crisp. A teneral crane fly is pale, soft and glossy for some hours after emergence.
• The wings are fully expanded and set, with the venation hardened and the pterostigma developed.

Not old either. The wear proxies are all at zero:

• All six legs present, with intact tarsi. This is the strongest of the four. Crane flies autotomise legs at the slightest provocation, and losses accumulate and are never repaired — a complete set implies a short and undisturbed adult life.
• Both wings entire. Margins smooth, no nicks, tears or fraying; the membrane is clean rather than greased or darkened.
• Both halteres present — small, exposed and easily lost.
• Antennal verticils complete, with no broken or missing bristles along either flagellum.

Two limits on that. Wear is a proxy, not a clock — it accumulates by chance as much as by time, so an unlucky fresh adult can lose a leg on its first night and a sheltered one can stay pristine longer than average. And this individual was indoors, on a smooth wall, out of wind and rain, which is a low-wear environment; the proxies will therefore tend to read younger than they would for an animal of the same age outdoors. The bracket should be taken as the direction of the evidence, not a measurement.

Identified reference photographs of T. paludosa and its closest look-alike, T. oleracea, against the same views of this specimen. These confirm genus and sex; they cannot pick the species, and the reason is visible at a glance.