Understanding the factors underlying sex differences in lifespan can provide valuable insights into lifespan evolution. Despite abundant species-level data, comparative studies on the drivers of sex differences in lifespan in invertebrates remain scarce compared with vertebrates. Here, we present a broad comparative analysis of sex differences in adult lifespan (SDL) in insects, using literature-derived data for 395 species spanning 17 orders. Across the dataset, female adults outlived males in 65 % of species, with a median lifespan 9 % longer than that of males. Mean lifespan was consistently female-biased across orders and functional groups, but the direction of SDL varied extensively at all taxonomic levels, even among congeneric species, consistent with the low phylogenetic signal observed for SDL (Pagel’s λ = 0.16). SDL was positively, albeit weakly, associated with sexual size dimorphism. Lifespan differences were generally more female-biased in functional groups where extended lifespan is expected to more strongly enhance female reproductive success, either because of time-consuming resource acquisition for egg production (e.g., predators) or prolonged search for oviposition substrates (e.g., parasitoids). Overall, our findings indicate that shared ancestry, sexual size dimorphism, and sex-specific selection pressures associated with reproductive ecology each contribute to variation in SDL, with no single factor clearly predominating.

Data collection

We aimed to collect data on sex differences in adult lifespan representing a taxonomically and ecologically broad range of insect species. Data were gathered from published case studies using two complementary approaches. The larger portion, roughly two-thirds of the data, was obtained through targeted searches in Google Scholar and Clarivate Web of Science conducted in 2023 and 2025. Since lifespan data are often reported as secondary outcomes and may not be mentioned in titles or abstracts, Google Scholar’s full-text search capability was particularly useful for locating such data. Our search queries included combinations of four generic terms that were neutral with respect to the magnitude and direction of our focal variable (i.e., SDL): one of several synonyms for adult lifespan (longevity, life span, lifespan), male*, female*, and insect* (or the name of a specific insect order). We used longevity as the primary synonym throughout, whereas other synonyms of adult lifespan were used only when searches with longevity and routine screening (see below) yielded insufficient data for a particular taxonomic group.

The rest of the data was collected by one of the authors through systematic screening of the tables of contents of a broad list of journals in entomology, ecology, and evolutionary biology. This effort involved both a one-time retrospective screening (conducted in 2003) and ongoing screening for articles published thereafter (until 2025). The screening process included regularly examining journals' tables of contents and reviewing the full-text of papers whose titles indicated they might contain relevant data. As lifespan data are typically presented in tables and figures, their identification within articles was generally straightforward. Because studies reporting sex-specific lifespan estimates in insects vary widely in their contexts, aims, and terminology for adult lifespan, assembling a complete set of published information for the more speciose and intensively studied orders (e.g., Lepidoptera, Coleoptera, Hymenoptera, Diptera) was not considered feasible from the outset. Although extensive, our dataset still should be regarded as a representative sample rather than complete record of the available data for these taxonomic groups. For smaller and less-studied orders, our targeted searches likely allowed us to assemble most of the published information on sex-specific adult lifespan. Inevitably, taxonomic and functional groups are not evenly represented in our dataset, reflecting differences in research focus as well as the practical challenges inherent to studying particular taxa. In total, we assembled sex-specific adult lifespan data for 395 insect species from 17 insect orders.

Where reported, sex-specific data on adult (or pupal) body size (preferably body mass) were extracted from the same studies reporting adult lifespan. Additional sex-specific body size data were derived from several previously published syntheses. Further body size data on specific species were obtained through targeted literature searches in Google Scholar using the species’ scientific name combined with relevant body mass-related terms (‘adult weight’, ‘adult mass’, ‘pupal weight’, ‘pupal mass’, ‘body size’).

Data extraction and criteria for eligibility

With the scope of the synthesis clearly defined, the eligibility of the identified studies was evaluated during the data collection process. The primary criterion for inclusion was that a study had to report mean values of both male and female adult lifespan of an insect species. Six studies presenting median values of lifespan were also accepted. Only laboratory-based data were considered, where major external sources of mortality, predators and parasitoids in particular, were explicitly excluded.

For a substantial proportion of species, lifespan data were available from multiple studies and/or multiple experimental treatments. To maximize comparability among species, we selected the dataset obtained under conditions that most closely approximated those considered optimal, rather than using all available datasets. Specifically, selection was based on the extent to which the experimental conditions met the following criteria: 1) ad libitum access to water and food, 2) the opportunity to mate, 3) the availability of an oviposition substrate (e.g., host plant), 4) the highest food quality (defined as the treatment associated with the highest larval survival, shortest development time, or largest body size, depending on the data available), and 5) an optimal temperature regime (assessed based on survival rates or conditions typical for the species’ biogeographic realm). When multiple datasets met these criteria equally well, priority was given to the dataset with the largest sample size. We explicitly excluded data from stress treatments, such as exposure to chill coma, heat shock, or biological and artificial toxins.

While we generally did not impose any taxonomic restrictions on the insects included in this study, we did not consider those with complex caste systems, such as ants, social bees and wasps. Also, we did not include a few studies in which the species' adult lifespan included diapause.

Volume-based measures (i.e., fresh or dry body mass) were the preferred metric for sex-specific body size, although linear measurements were also accepted when body mass data were unavailable. When body size and lifespan data were reported together, both were extracted from the same study and treatment. If size data came from a different study, we used data from treatments where the conditions for juvenile development were likely closest to optimal. The choice of treatment was guided primarily by measures of pre-adult survival (egg-to-adult, larval-pupal, or larval, depending on availability) or, when survival data were unavailable, by juvenile development time. Both metrics are commonly used indicators of developmental environment in insects, with higher survival and shorter development time generally reflecting more benign (laboratory) conditions. Although SSD can show some population-level variation within species, it is typically limited relative to the variation observed among insect species.

Graphically presented lifespan and body size data were extracted using WebPlotDigitizer 4.3.

Species were categorized into functional groups, where possible, based on the feeding ecology of their adult and larval stages.

Deriving SDL and SSD values from collected data

For each species, we calculated the natural logarithm of the ratio of mean female to mean male adult lifespan. This metric served as the effect size quantifying sex differences in adult lifespan (SDL) in our meta-analytic models. The resulting species-specific SDL values are symmetrically distributed around zero, with SDL = 0 indicating no sex difference in adult lifespan, and positive and negative SDL values indicating female-biased and male-biased lifespan, respectively. This choice of effect size permits direct calculation of the standard error of SDL when the standard errors of the sex-specific means are available, as was the case for most species in our dataset.

SSD was quantified using the widely used algorithm of Lovich and Gibbons (1992): [(size of the larger sex) / (size of the smaller sex)] – 1, with a positive sign assigned to the resulting values when females are larger and a negative sign when males are larger. Because body size was reported either as body mass (85 % of the 266 species included in the meta-analysis) or as various linear measurements, we standardized all size data to ensure comparability of SSD estimates across species. When body mass was available, it was used directly in the calculations. When only linear measurements (e.g., body length, head width) were available, these were converted to mass equivalents prior to estimating SSD. In particular, when body length was provided, we used published taxon-specific allometric equations to estimate body mass. For other linear size measures lacking appropriate allometric relationships, we applied cube transformation to approximate mass under isometric scaling assumptions before calculating SSD.