FIGURE 1. Burrowing arthropod predators investigated in this study. A) Scolopendra viridis, B) Scolopendra polymorpha, C) Hemiscolopendra marginata, D) Hadrurus arizonensis, E) Smeringurus mesaensis, F) Uroctonus mordax, G) Heterometrus spinifer, H) Pandinus imperator, I) Mastigoproctus giganteus, J) Hogna lenta, K) Gorgyrella inermis, L) Myrmekiaphilia sp., M) Aphonopelma chalcodes, N) Hysterocrates gigas, and O) Pelinobus muticus.
FIGURE 2. Examples of experimental enclosures used in this study. A) Surface view of a 212 L enclosure before the introduction of the study animal. Objects were placed on the surface to encourage burrowing. B) Side view of a 246 L enclosure filled with 60 cm of an organic rich clay loam. C) A 212 L enclosure filled with 55 cm of an organic-rich clay loam. Five specimens of Pandinus imperator produced a branching burrow complex in the subsurface (at arrow). D) Plaster-filled, connected U-shaped burrows produced by Mastigoproctus giganteus in a 38 L enclosure filled with an organic-rick clay loam.
FIGURE 3. Quantitative burrow properties. A) Measurements were taken for number of surface openings (SO), burrow slope (S), maximum depth (D), total length (L), tunnel, shaft, and chamber width (w), height (h), and circumference (c), and branching angles (BA). B) Complexity includes the number of segments (s), chambers (h), and surface openings (e) within a single burrow system. C) Tortuosity of a single burrow segment is found by dividing the total length (u) by the straight-line distance (v) from end to end. Modified from Hembree (2019).
FIGURE 4. Burrowing techniques observed among the studied arthropod predators. A) Initial burrowing by intrusion by Scolopendra polymorpha (burrow opening at arrow). B) Burrowing by intrusion by Hogna lenta. C) Continued construction of a vertical shaft by compression by Gorgyrella inermis, compressing sediment along burrow boundary (at arrow) to increase the width. D) Subsurface tunnel construction by intrusion by Hemiscolopendra marginata. No sediment is removed as the tunnel is extended but is pressed against the tunnel boundary (at arrow). E) Burrowing by excavation by Mastigoproctus giganteus. Sediment is removed and carried with the pedipalps (at arrow). F) Burrowing by excavation by Pelinobus muticus. Sediment is removed and carried with the pedipalps (at arrow). G) Burrowing by excavation by Hadrurus arizonensis. Sediment is scraped and kicked back out (at arrow) of the developing burrow with the first two pairs of legs. H) Backfilling of a tunnel by S. polymorpha. The centipede removes sediment from the developing tunnel and uses it to fill the old tunnel (at arrow). I) Light silk lining around the opening, shaft, and chamber (at arrows) of Hysterocrates gigas. J) Thick silk lining around the shaft (at arrow) of G. inermis producing a smooth interior surface. K) Six silk runners (example at arrow) connected to the burrow entrance of G. inermis with a closed trap door.
FIGURE 5. Burrow-associated activities and behaviors observed among the studied arthropod predators. A) Hysterocrates gigas (at arrow) dwelling within a shallow burrow with an enlarged terminal chamber. B) Two specimens of Pandinus imperator dwelling within a burrow complex. C) Scolopendra polymorpha moving through a burrow complex. D) Scolopendra polymorpha engaged in ambush predation positioned just below the burrow opening. E) Hysterocrates gigas engaged in ambush predation braced within the vertical shaft below the burrow opening. F) Aphonopelma chalcodes (at arrow) waiting within its burrow for prey to enter the tunnel. G) Pandinus imperator (at arrow) waiting within its burrow for prey.
FIGURE 6. Burrow morphology: openings and architecture. A) Elliptical burrow opening of Scolopendra polymorpha. B) Circular burrow opening of Hysterocrates gigas surrounded by a mound of excavated sediment. C) Paired triangular burrow openings of Pandinus imperator. D) Simple vertical burrow of Gorgyrella inermis with a single entrance. E) Vertical branching burrow of Pelinobus muticus with a single entrance. F) Vertical burrow Hysterocrates gigas with large terminal chamber and a single entrance. G) Subvertical helical burrow of Aphopelma chalcodes with a single entrance. H) J-shaped burrow of Mastigoproctus giganteus with a single entrance. I) U-shaped burrow of M. giganteus with two entrances. J) Y-shaped burrow of M. giganteus with two entrances. K) Mazework of M. giganteus with five entrances (at numbers). L) U-shaped burrow of S. polymorpha with two entrances. M) Mazework of S. polymorpha with four entrances (at numbers).
FIGURE 7. Burrow morphology: architecture and bioglyphs. A) Simple subhorizontal burrow of Hadrurus arizonensis with a single entrance. B) Helical subhorizontal burrow of H. arizonensis with a single entrance. C) Simple subhorizontal burrow of Pandinus imperator with a single entrance. D) Branching subhorizontal burrow of P. imperator with a single entrance. E) Branching, helical burrow of P. imperator with a large terminal chamber (at arrow). F) Mazework of H. arizonensis with multiple branches and two entrances (at arrows). G) Multiple, fine striations (at arrows) along, and parallel to, the shaft of a Gorgyrella inermis burrow. H) Pair of protrusions (at arrows) on the roof of a terminal chamber of Mastigoproctus giganteus. I) Large striations (at arrows) along the side of a subhorizontal burrow of Aphonopelma chalcodes. J) Burrow opening of Hogna lenta showing silk and sediment lining (at arrow). K) Compression lining (at arrow) visible in a cross section of a tunnel of Scolopendra
polymorpha.
