Intruder alert: Factors influencing the success of maternal nest defense against conspecific egg cannibalism in the maritime earwig
Data files
Apr 29, 2026 version files 42.41 KB
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Cannibalism_Data_with_both_egg_counts.csv
13.62 KB
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Overall_Combined_Nests_Behavior_Summary.csv
14.10 KB
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Overall_Successful_Nests_Behavior_Summary.csv
6.80 KB
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README.md
7.89 KB
Abstract
Parental care is relatively rare in insects, where parents typically maximize the number of offspring produced rather than investing in individual offspring survival. However, some insects do guard nests or clusters of eggs against predation risk or when conspecifics pose a threat of cannibalizing offspring. The maritime earwig (Anisolabis maritima; Order Dermaptera), an insect found under objects above the high tide line, exhibits nest guarding against cannibalistic conspecifics. Because both male and female cannibals exhibit size-based aggression but differ in morphology and temperament, we studied how different intruder characteristics influenced the success of maternal nest defense. Although mothers were usually effective in protecting their eggs, we found that both the relative size and the sex of conspecific intruders affected the mother’s behavior and success in egg guarding. Specifically, we found that mothers were more successful in defending their eggs against smaller opponents and against females. Our results may reflect that smaller opponents are generally less aggressive and that females are less likely to invade nests than males. This study provides insight to how the benefits of maternal care in response to cannibalism are likely to depend on the sex ratio and size distribution of the colony.
Cannibalism_Data_with_both_egg_counts.csv
This file contains trial-level observations from a cannibalism experiment examining egg consumption under different intruder conditions.
Each row represents a single trial, with 126 observations across 17 active columns (5 trailing empty columns are present and can be disregarded).
Experimental Design
Each trial paired a resident mother with an intruder individual under one of six treatment conditions, varying intruder size (small, same, large)
and intruder sex (female or male):
- Small Female
- Same Female
- Large Female
- Small Male
- Same Male
- Large Male
Approximately 20–22 trials were conducted per treatment group.
Column Descriptions
- Mother ID – Unique identifier for the resident female
- Mother Pronotum Width (mm) – Body size measurement of the resident mother
- Date Start / Time Start – Date and time the trial began
- Date Stop / Time Stop – Date and time the trial ended
- Camera/Station – Recording station identifier (1–4)
- Treatment – Treatment group label indicating intruder size and sex
- Intruder ID – Unique identifier for the intruder individual
- Intruder Size – Size class of the intruder (Small, Same, or Large relative to the mother)
- Intruder Sex – Sex of the intruder (F or M)
- Egg Count Start – Number of eggs present at the beginning of the trial
- Egg Count End – Number of eggs present at the end of the trial
- Eggs Eaten – Number of eggs consumed during the trial (calculated as the difference between start and end counts)
- Who Consumed? – Identity of the individual responsible for egg consumption: mother, intruder, both, or N/A (no consumption occurred)
- % Eggs Consumed – Proportion of eggs consumed during the trial
- Success – Binary outcome indicating whether the trial was completed successfully (Successful or Unsuccessful)
Notes: Size was measured in mm (pronotum width).
Overall_Combined_Nests_Behavior_Summary.csv
This file contains trial-level behavioral summaries from a nest intrusion experiment examining how resident mothers respond to intruders of varying size and sex. Each row represents a single trial, with 125 observations across 23 columns. The dataset shares its experimental design and initial trial metadata with the cannibalism dataset, with the addition of detailed behavioral outcome variables.
Experimental Design
Each trial paired a resident mother with an intruder under one of six treatment conditions, varying intruder size (small, same, large) and intruder sex (female or male):
- Small Female
- Same Female
- Large Female
- Small Male
- Same Male
- Large Male
Approximately 20–22 trials were conducted per treatment group.
Column Descriptions
Trial Metadata (shared with cannibalism dataset)
- Mother ID – Unique identifier for the resident female
- Mother Pronotum Width (mm) – Body size measurement of the resident mother
- Date Start / Time Start – Date and time the trial began
- Date Stop / Time Stop – Date and time the trial ended
- Camera/Station – Recording station identifier; used for bookkeeping
- Treatment – Treatment group label indicating intruder size and sex
- Intruder ID – Unique identifier for the intruder individual
- Intruder Size – Size class of the intruder (Small, Same, or Large relative to the mother)
- Intruder Sex – Sex of the intruder (F or M)
- Egg Count Start – Number of eggs present at the beginning of the trial
Trial Outcome Variables
Nest Type – Outcome of the nest trial: Successful (mother retained nest, n = 77) or Unsuccessful (mother lost nest, n = 49)
Behavioral Count Variables
All behavioral variables represent total counts of each behavior observed during the trial.
- Mating? - Whether or not a mother mated with the intruder. For male intruders, values were either "1" (mating occurred) or "0" (mating did not occur). For female intruders, all values were marked as "N/A" or "Not Applicable" in that mating was not possible with the mother (same-sex pairings).
- Aggressive Interaction Total – Total number of aggressive interactions (range: 0–96)
- Basic Interaction Total – Total number of non-aggressive, non-incidental interactions (range: 0–98)
- Cohabitation Total – Total number of cohabitation events, where both individuals occupied the nest simultaneously (range: 0–88)
- Invasion Total – Total number of intruder nest entry events (range: 0–47)
- Leave Total – Total number of events in which one individual left the nest (range: 0–64)
- Mating Total – Total number of mating events observed during the trial (range: 0–8)
- Mating Total after Consumption – Total number of mating events occurring after any egg consumption event (range: 0–5)
- Filtered Mating after Consumption – Subset of post-consumption mating events meeting additional filtering criteria, as described in Methods (range: 0–4)
- Filtered Mating Total – Subset of all mating events meeting filtering criteria (range: 0–5)
Notes
The trial metadata columns in this file correspond directly to those in the cannibalism dataset and can be used to link observations across files by Mother ID and trial date.
Overall_Successful_Nests_Behavior_Summary.csv
This file is a subset of the combined nests behavioral dataset, containing only the 77 trials in which the resident mother successfully retained her nest.
Each row represents a single successful trial across 17 columns. It shares the same column structure as the combined dataset but omits the Mother Pronotum Width, Egg Count Start, and Nest Type columns.
Experimental Design
The same six treatment conditions are represented, though trial counts per group are unequal due to subsetting by nest outcome:
- Small Female (n = 20)
- Same Female (n = 15)
- Large Female (n = 8)
- Small Male (n = 14)
- Same Male (n = 13)
- Large Male (n = 7)
The lower representation of large intruder treatments reflects that larger intruders more frequently displaced the resident mother,
resulting in fewer successful trials in those groups.
Trial Metadata
- Mother ID – Unique identifier for the resident female
- Date Start / Time Start – Date and time the trial began
- Date Stop / Time Stop – Date and time the trial ended
- Camera/Station – Recording station identifier; used for bookkeeping
- Treatment – Treatment group label indicating intruder size and sex
- Intruder ID – Unique identifier for the intruder individual
- Intruder Size – Size class of the intruder (Small, Same, or Large relative to the mother)
- Intruder Sex – Sex of the intruder (F or M)
Behavioral Count Variables
All behavioral variables represent total counts of each behavior observed during the trial.
- Mating? - Whether or not a mother mated with the intruder. For male intruders, values were either "1" (mating occurred) or "0" (mating did not occur). For female intruders, all values were marked as "N/A" or "Not Applicable" in that mating was not possible with the mother (same-sex pairings).
- Aggressive Interaction Total – Total aggressive interactions (range: 0–94)
- Basic Interaction Total – Total non-aggressive interactions (range: 0–69)
- Cohabitation Total – Total cohabitation events (range: 0–43)
- Invasion Total – Total intruder nest entry events (range: 0–47)
- Leave Total – Total nest-leaving events (range: 0–64)
- Mating Total – Total mating events observed; recorded as N/A for female intruder trials (range among male intruder trials: 0–8)
Notes
This file can be linked to the combined nests dataset and the cannibalism dataset by Mother ID.